Need for #944

Check that:
 - Error writing to vylog does not break vinyl permanently.
 - An index drop/truncate/create record that was not written to vylog
   due to a write error is buffered and flushed along with the next
   write.
 - A buffered index drop/truncate/create record that hasn't been flushed
   before restart is replayed on WAL recovery.

Closes #2490

Add box.atomic(fun, arg) wrapper to execute fun(arg) in a transaction.

Closes #818

Closes #2522

* Add string.hex() method
* Add hmac.*_hex to crypto.lua
* Update crypto/digest to use string.hex()

Closes #2510

Replace the following index.info fields

  memory_used           # size of statements in memory
  size                  # size of statements on disk
  count                 # number of statements on disk and in memory
  page_count            # number of pages on disk

with

  memory
    rows                # number of statements in memory
    bytes               # size of statements in memory

  disk
    rows                # number of statements on disk
    bytes               # size of statements on disk (unpacked)
    bytes_compressed    # size of statements on disk (packed)
    pages               # number of pages on disk

  rows                  # total number of all statements
  bytes                 # total size of all statements

To achieve that, this patch introduces new classes that can be used for
accounting statements on disk and in memory, vy_stmt_disk_counter and
vy_stmt_counter, and makes vy_slice, vy_run, vy_range, and vy_index use
them instead of counting rows, bytes, and pages directly. The difference
between the two classes is that vy_stmt_counter only accounts rows and
bytes, while vy_stmt_disk_counter also includes bytes_compressed and
pages. The classes will be reused for accounting reads and writes later.

Needed for #1662

 - Delete unused vy_page_info->min_key_offset.
 - Move vy_run_info->{size,keys,page_infos} to vy_run, because
   they are not a part of run info stored in .index file.
 - Rename vy_run->page_infos to page_info.
 - Rename vy_page_info->count, vy_run->keys, and vy_slice->keys
   to row_count.
 - Update comments.

It's no use having a separate method for every kind of integer we want
to append to box info - int64_t should suit everyone.

We compute dump bandwidth basing on the time it takes a run writing task
to complete. While it used to work when we didn't have data compression
and indexes didn't share in-memory tuples, today the logic behind dump
bandwidth calculation is completely flawed:

 - Due to data compression, the amount of memory we dump may be much
   greater than the amount of data we write to disk, in which case dump
   bandwidth will be underestimated.

 - If a space has several indexes, dumping it may result in writing more
   data than is actually stored in-memory, because tuples of the same
   space are shared among its indexes in-memory, but stored separately
   when written to disk. In this case, dump bandwidth will be
   overestimated.

This results in quota watermark being set incorrectly and, as a result,
either stalling transactions or dumping memory non-stop.

Obviously, to resolve both issues, we need to account memory freed per
unit of time instead of data written to disk. So this patch makes
vy_scheduler_trigger_dump() remember the time when dump was started and
vy_scheduler_complete_dump() update dump bandwidth basing on the amount
of memory dumped and the time dump took.

Currently, vy_scheduler_remove_mem() calls vy_scheduler_complete_dump()
if vy_scheduler_dump_in_progress() returns false, but the latter doesn't
necessarily mean that the dump has just been completed. The point is
that vy_scheduler_remove_mem() is called not only for a memory tree that
has just been dumped to disk, but also for all memory trees of a dropped
index, i.e. dropping an index when there's no dump in progress results
in vy_scheduler_complete_dump() invocation. This doesn't do any harm
now, but looks ugly. Besides, I'm planning to account dump bandwidth in
vy_scheduler_complete_dump(), which must only be done on actual dump
completion.

Following patches will add more logic to them, so it's better to factor
them out now to keep the code clean. No functional changes.

Currently, to force dumping all in-memory trees, box.snapshot()
increments scheduler->generation directly. If dump is in progress and
there's a space that has more than one index and all its secondary
indexes have been dumped by the time box.snapshot() is called and its
primary index is being dumped, incrementing the generation will force
the scheduler to start dumping secondary indexes of this space again
(provided, of course, the space has fresh data). Then, creating a dump
task for a secondary index will attempt to pin the primary index - see
vy_task_dump_new() => vy_scheduler_pin_index() - which will crash,
because the primary index is being dumped and hence can't be removed
from the scheduler by vy_scheduler_pin_index():

  Segmentation fault
  #0  0x40c3a4 in sig_fatal_cb(int)+214
  #1  0x7f6ac7981890 in ?
  #2  0x4610bd in vy_scheduler_remove_index+46
  #3  0x4610fe in vy_scheduler_pin_index+49
  #4  0x45f93e in vy_task_dump_new+1478
  #5  0x46137e in vy_scheduler_peek_dump+282
  #6  0x461467 in vy_schedule+47
  #7  0x461bf8 in vy_scheduler_f+1143

To fix that let's trigger dump (by bumping generation) only from the
scheduler fiber, from vy_scheduler_peek_dump(). The checkpoint will
force the scheduler to schedule dump by setting checkpoint_in_progress
flag and setting checkpoint_generation.

Closes #2508

The replace trigger of _truncate system space (on_replace_dd_truncate)
does nothing on insertion into or deletion from the space - it only
updates space truncate_count when a tuple gets updated. As a result,
space truncate_count isn't initialized properly after recovering
snapshot. This does no harm to memtx, because it doesn't use space
truncate_count at all, but it breaks the assumption made by vinyl that
if space truncate_count is less than index truncate_count (which is
loaded from vylog), the space will be truncated during WAL recovery and
hence there's no point in applying statements to the space (see
vy_is_committed_one). As a result, all statements inserted into a vinyl
space after snapshot following truncation of the space, are ignored on
WAL recovery. To fix that, we must initialize space truncate_count when
a tuple is inserted into _truncate system space.

Closes #2521

Inpspired by tarantool/curl module by Vasiliy Soshnikov.
Reviewed and refactored by Roman Tsisyk.

Closes #2083

Rename `struct type` to `struct type_info` and `struct method` to
`struct method_info` to fix name clash with curl/curl.h

We added _truncate space to 1.7.5 and we are going to add new system
spaces for storing sequences and triggers. Without upgrade, the
corresponding operations won't work. Since 1.7.5 is a minor upgrade,
users may not call box.schema.upgrade(), so we need to call it for them
automatically. This patch introduces infrastructure for automatic
upgrades and sets upgrade to 1.7.5 to be called automatically.

While we are at it, rename schema version 1.7.4 to 1.7.5 (1.7.4 has
already been released).

Closes #2517

Follow up #2496

Set checkpoint_count = 2, checkpoint_interval = 3600 by default.

vinyl/layout.result is updated because checkpoint_count was changed
from 6 to 2.

Closes #2496

If more than one request rollbacks then vclock_follow cause
commit broken order

Compiling with arm raises a signed and unsigned comparison error.

Do not call vy_mem_older_lsn on each UPSERT commit. Older lsn
statement is used to squash big count of upserts and to turn
UPSERT into REPLACE, if the older statement has appeared to be
not UPSERT.
But n_upserts could be calculated on prepare phase almost free,
because the bps has method bps_insert_get_iterator, which
returns iterator to the inserted statement. We can move this
iterator forward to the older lsn without searching in the tree and
update n_upserts.

On a commit phase we can get the n_upserts, calculated on a prepare
phase, and call vy_mem_older_lsn only if there is a sense to
optimize the UPSERT.

Closes #1988

According to the code, 'replace' tuple can also have UPSERT type.
Lets name it 'repsert' = 'replace' + 'upsert'.

Improve the error message when selecting from HASH index using
a partial key.

Fixes gh-1463.

tuple_field_...() is a family of functions for retrieving a field
from tuple with checking of the specified type. Implement no-throw
versions of these functions to use them from C code.

Needed #944

Needed for #944 and #2285

Set of error injection before issuing a select, to avoid its
effects on select execution.

Fix a typo in a status message (gh-2417)

Space should not be accessible while droping. See #2075

A new record type has been added to vylog by commit 353bcdc5
("Rework space truncation"), VY_LOG_TRUNCATE_INDEX. Update the test.

Since vinyl files (run, index, vylog) don't have space id, reading them
with tarantoolctl-cat fails with:

  tarantoolctl:784: attempt to compare nil with number

In case of failure, print files that were not deleted and
the output of box.internal.gc.info().

Needed for #2486

To match box.cfg.vinyl_read_threads introduced by the previous patch.