Different fibers had shared connection structure - sqlite3 * db.
It had several variables that were shared between transactions in
fibers.

- Move db->autoCommit flag into VDBE
- Move db->isTransactionSavepoint into VDBE
- Move savepoints to VDBE and related counters from struct sqlite3
- Make transactions savepoints local according to VDBE

Closes #2668

- In Tarantool there are no limit on space identifier. Check that there
are also no limit on name lengths in SQL.

- Implement sql-tap/gh2127-identifier-max-length.test.lua

Closes #2127

SQLite backup and shell are unnecessary elements, there is no
sense in keeping it in our project.

- Remove src/box/sql/backup.c .
- Remove src/box/sql/shell.c .

Also, fix output for sql/on-conflict

- ON CONFLICT work checked:
Works correctly (not including ROLLBACK, because sql transactions
are not implemented now)
- Tests for ON CONFLICT implemented

Now system space formats contain conflicts between space:format,
their index parts and actual tuple fields.

Such formats can not be used to check tuple fields in SQL.

Fix them in order of #2652

strlen() can not be called on message pack auth data. Besides, auth
data can be not only string, but also array or map. And if
array/map is empty, strlen() returns > 0 - it is incorrect.

Needed for #2652

- Use malloc() as a fallback for lsregion for large size
- Set Vinyl slab_size to 16Mb and don't use vinyl_max_tuple_size
  for calculation
- Allow dynamic configuration of vinyl_max_tuple_size

A part of #2342

On 64-bit iconv called via ffi returns a uint64_t cdata object, which
equals to -1 in case of error so error handling works fine. On 32-bit it
returns a number equal to (size_t)-1, which is equal to 4294967295 and
not equal to -1 when compared to in Lua. As a result Lua binding to
iconv hangs if the source string is incorrect. Fix this by comparing the
result of iconv to ffi.cast('size_t', -1) instead of -1.

Closes #2466

Follow up #2334

An on_replace trigger on replica can issue local changes
using its own replica_id. Check replica_id for every row
during writing to WAL.

Fixes #2682

Fix minor issues found by coverity scan:
 - Do not try to estimate slice size if the run is empty to avoid div/0.
 - Fix assert() that is supposed to check slice->first_page_no, but
   checks last_page_no instead.
 - If the slice doesn't intersect with the run (i.e. slice->end is less
   than or equal to run->begin), leave its stats zeroed out.

Closes #2698

The bug happens when some TX deletes a statement (writes it to
its own write set) and then reads a range of tuples containing
that deleted statement. DELETE must not come to select result
(in this and only transaction before it is committed) and
just are skipped by read iterator. After such a skipping and
getting next true (non-DELETE) statement the iterator considers
that there is no data between the previous statement and the
current, and add them to the cache as a chain. This is wrong
because the data could be hidden by DELETE statement.

Track such jumps over TXW DELETE statements in read iterator and
do not add statements as a chain in this case.

We use a binary tree for tracking reads (read_set). The tree is ordered
by (index, statement, tx). Insertion of a partial statement into the
tree may result in breaking comparison transitivity, which is mandated
by the tree implementation. However, for range requests we insert the
search key into the read set, which may be partial. This may result in a
crash in the read_set.

Tracking the search key doesn't make much sense anyway: it doesn't bring
us any closer to range request tracking, only obscures the semantics of
select. So let's track only statements actually returned by the iterator
plus gaps found by point requests.

Closes #2675

Fix bad merge of 945a97db and 7a5835f4

A dump task can be scheduled or completed after we saved stats.
Make sure this doesn't happen.

Closes #2696

Do not use thumb specifier for asm code, use unified syntax directive
instead.

Revoke permissions granted by the test.

Needed for #946

Relay reader fiber is jonable now and should be joined by relay main
fiber.
See #2284

Don't stop coio twice.

Update comments.

Replication slave send its current vclock to replication master
after recieving new data from master.
See #2284

There is a check in vy_point_iterator_apply_history that compares
statement's lsn with lsn with vlsn and skips history node if the
statement is invisible.

This check is wrong:
 - if TX was originally in a read view it could not read any
invisible statement.
 - if TX was not in a read view but were sent to read during yield,
the new created read view must see all current database state,
including data that was read by the iterator.
 - if TX is in read view and made some changes (in own TX write
set) it will skip TXW statement since it has INT64_MAX lsn.

Replace check with assert. Concern possibility of TXW statement.

Write appropriate test.

test/small symlink was created only on `make test`,
create this symlink `make all`.

Check current user write access on space truncate.

Fixes #2674

_truncate space write access is required for space truncation.
Add this privilege to bootstrap.snap.

See #2674

Closes #2609
Closes #2633
Closes #2616

Follow up #910