As index_size does not match row count for vinyl engine,
it was replaced with index_count that working for
ITER_ALL in memtx same way.

Part of #2199.

Part of #2199.

@TarantoolBot document
Title: new pragma sql_default_engine
Now it is allowed to create vinyl spaces using special pragma
setting default engine for SQL requests.
This config is stored in user_session() and affect *only*
tables been created with SQL.
Example:
\set language sql
pragma sql_default_engine='vinyl';
CREATE TABLE t3(a primary key,b,c);

To follow ANSI SQL standard we should dissallow returning
multiple rows from subselects after = and in braces ().
To achieve this goal we have introduced Select SF_SingleRow
flag that indicates the case of subselect having no
client-defined LIMIT 1 to patch system implicit LIMIT 1 to
be LIMIT 2 and generate extra bytecode to HALT execution on
reaching this restrict.

Resolves #2366.

IPROTO_OPTIONS (2.0) and IPROTO_SERVER_IS_RO (1.10) use the same key
code (0x29). Resolve this conflict by moving IPROTO_OPTIONS to 0x2a.

fiber->on_yield triggers were not invoked in fiber_call(),
which meant that memtx transaction was not rolled back by
fiber.create().

Fixes gh-3493

Part of #3328

Analyze samples are encoded with msgpack and should be decoded as a
msgpack.

sqlite3Stat4Column sqlite-style function converted to sql_stat4_column
Tarantool-styled.

Closes #2860

As new _trigger format contains space_id, we can avoid
storing AST pointers in HASH. Requested AST could be found
by name in appropriate space.

Part of #3273.

Trigger presence in system should be tested on each VDBE
execution attempt, not on Parser iteration as system state
could be changed between opcode run.
With this patch, such checks are the part of VDBE program
looking to the _trigger space and raise error message if
tuple with specified key already exists.

Part of #3435, #3273

Changed Trigger structure name to sql trigger to avoid
confusing similarity with Tarantool trigger structure.
Refactored related code to match tarantool codestyle.

Part of #3273.

Introduced sql_triggers field in space structure.
Changed parser logic to do not insert built triggers, just only
to do parsing. All triggers insertions and deletions are operated
via on_replace_dd_trigger now.
Global DB hash has been kept as we still ned to get Trigger AST
by name on trigger deletion.

Resolves #3273.

As we would like to lookup triggers by space_id in future
on space deletion to delete associated _trigger tuples we
need to introduce new field space_id as secondary key.

Part of #3273.

As error codes were not sorted, changing any of error
constants significantly change test case output. This
cause unnecessary changes on each such commit.

As we are going to port triggers to server, we need
an instrument to release allocated memory in alter.cc.

Part of #3273.

`sql_current_time` is exported only in debug mode and used to check
builtin datetime sql functions behavior in specific time moments.

Extra changes:
 * table-14.1 test is deleted, as it does not test anything.
   It was testing ddl inside of a transaction. This case is checked
   by 14.2 by now.

Closes #2646

Make RANDOMBLOB(0) return NULL, it was returning random
blob of length 1 before. Allow rounding to more than 30
digits.

Part of #2347

If we ever will have extensions support, it will be
impemented in different way. Remove this legacy code.

Closes #2183

Removed legacy functions: sqlite_version, sqlite_sourceid,
sqlite_log. Added version built-in function which returns
Tarantool's version.

Closes #2184

Bug: During parsing http headers, long headers names are truncated
to zero length, but values are not ignored.

Fix this with adding parameter  max_header_name_length to http request.
If header name is bigger than this value, header name is truncated to
this length. Default value of max_header_name_length is 32.

Do some refactoring with renaming long names in http_parser.

Closes #3451

Bug: Header parser validates http status line and besides saving http
status, saves valid characters to header name, which is wrong.

Fix this with skipping status line after validation without saving it as
a header.

In scope of #3451

If tarantool is stopped while writing a snapshot or a vinyl run file,
inprogress files will never be removed. Fix this by collecting those
files on recovery completion.

Original patch by @IlyaMarkovMipt. Reworked by @locker.

Closes #3406

In order to log only about files that were actually removed change log
messages from "removing <name of file>" to "removed <name of file>" in
vy_run_remove_files and xdir_collect_garbage functions.

Needed for #3406

Update expander of SELECT statement to search for space if
corresponding table wasn't found in table hash. Create dummy
table if so and fill def field only.

Also fix a leak in VIEW creation.

Part of #3369

A minor follow up on the fix for gh-3452 (http.client timeout bug)

Current implementation of http.client relies on fiber_cond which is set
after the request was registered and doesn't consider the fact that
response may be handled before the set of fiber_cond.

So we may have the following situation:
1. Register request in libcurl(curl_multi_add_handle in curl_execute).
2. Receive and process response, fiber_cond_signal on cond_var which no
one waits.
3. fiber_cond_wait on cond which is already signaled. Wait until timeout
is fired.

In this case user have to wait timeout, though data was received
earlier.

Fix this with adding extra flag in_progress to curl_request struct.
Set this flag true before registering request in libcurl and set it
false when request is finished before fiber_cond_signal.
When in_progress flag is false, don't wait on cond variable.

Add 1 error injection.

Closes #3452

schema_version must be passed to perform_request in 1.9

When a connection is closed, some of long-poll requests still may
by in TX thread with non-discarded input. If a connection is
closed, and then an input is discarded, then connection must not
try to read new data.

The bug was introduced here:
f4d66dae by me.

Closes #3400

IPROTO_SERVER_IS_RO currently has code 0x07 and is defined in the header
key section, which is wrong, because this key is only used in request
body. Let's move it to the body section, where it belongs, and set its
code to 0x29. This shouldn't break anything even if 0x07 is reused in
future, because the two codes belong to different sections and hence are
never parsed in the same function. Worst that can happen is we fail to
bootstrap a node in the cluster if it is running a newer tarantool
version.

While we are at it, let's also add the key name and change its type from
MP_UINT to MP_BOOL.

Fixes commit a8ecd1e1 ("replication: fix bug with read-only replica
as a bootstrap leader").

Throughout the code, we return -1 on error, but decode methods return 1
for some reason, although according to comments they are supposed to
return -1. This doesn't result in any errors, because we use != 0 to
check for errors. Nevertheless, let's fix it to avoid confusion.

When reopening an existing xlog file (as in case of vylog), we do not
erase the eof marker immediately. Instead we reposition file offset
to (file_size - sizeof eof_marker), assuming the eof marker will be
overwritten on the first write.

However, it isn't enough if we want to reuse this function for reopening
WAL files, because when scanning the WAL directory we close a file if we
read eof marker and never reopen it again, see recover_remaining_wals().
So to avoid skipping rows written to a once closed WAL, we have to erase
the eof marker when reopening an xlog file. Let's do it with truncate().

If a source is used on a read iteration (i.e. the key at which it is
positioned is the next best match or, in terms of the read iterator
implementation, its front_id matches the read iterator front_id), its
history is cleaned up, see vy_read_iterator_apply_history(). This breaks
the logic behind vy_read_src_is_behind(), which assumes that the history
always points to the last used key. As a result, a source may be
mistakenly skipped, as illustrated below:

  Fiber 1                               Fiber 2
  -------                               -------
  1. Opens read iterator.
  2. Advances it to the next key.
     The returned key was read from
     a mem or run (not from cache).
     The source's history is emptied.
                                        Adds a chain containing
                                        the key read by fiber 1
                                        to the cache.
  3. Continues iteration, reads
     next few keys from the cache
     until the chain ends. The source
     used at step 2 is skipped.
  4. Calls vy_read_src_is_behind()
     on the source used at step 2 and
     skipped at step 3. It returns
     false, because its history is
     empty, thus skipping keys stored
     in it.

Fix this bug by moving the code that checks whether a source iterator
needs to be advanced from vy_read_src_is_behind() to source iterator
'skip' method, because there we always know the last key returned by
the iterator.

Basically, this returns the code we had before commit b4d57284
("vinyl: consolidate skip optimization checks in read iterator").

Closes #3477

Allow define access privileges for all spaces, functions and sequences.
Read and write privileges are supported for spaces, execute privilege
for sequences. Privilege granting and revoking might be done through old api
without object identification:
  box.schema.user.grant("guest", "read", "space")

Prerequisite #945