* provide savepoint API, for statement-level rollback
* don't implicitly rollback entire transaction in console (this
  breaks a fix for gh-817 + memtx, but it's the least of two
  evils when working with console - not usable transactions in vinyl vs
  inconsistent behavior of transactions in memtx

* prepare for removal of tx_index, move all dependent declarations
up for that purpose
* vinyl_rollback returns void

Fixes #1664

Fixes #1602

Fixes #1663

Change mkdir() mode to 0777 to be consistent with WAL writer and
snapshot dumper which use 0666 for files.
umask is applied as usual.

Fixes #1571

Try to increase readability of vy_apply_upsert().

Fixed incorrect update ops checking in vinyl
and memtx.
Fixes #1650

https://github.com/tarantool/build/issues/16

* the conflict manager index is used only in the tx thread.

Don't maintain the number of writes, it's broken in case
of a savepoint rollback, and is implicitly known from a non-empty
write log.

* yes, they shouldn't have been there in the first place

* the structure for 3 members was a bit of over-engineering;
* 2 ouf of the 3 members are themselves scheduled for removal

* replace vy_buf with stailq

* inline txlogindex_replace
* remove SVCONFLICT flag from tuple

* in preparation with replacement of array with a linked
  list, remove txlog_count().

* use a pointer to transaction value instead of a numeric
offset

Fixes #1440

* the bug with iobuf recycling has always been in 1.6,
  and is fixed in 1.7, but got more exposure with the patch
  for gh-846. "Idle" state of iobuf was calculated incorrectly.

* update comments
* coding style
* avoid using delete + inserts or delete + replace
  if replace  alone is enough.

Fixes gh-623.

An implementation for both unique and non-unique
secondary indexes for vinyl storage engine.
engine.

Tests for secondary indexes were added to 'engine' test suite.

* only run the garbage collector in tx manager if there are
  conditions for it.

- Remove useless abstraction layers
- Extract explicit vy_task structure from code
- Fix #1558: occasional crashes after dropping index

Needed for #1592

* remove a separate counter for commit sequence
  number, put transaction start and end time on the same logical
  clock scale

Package.searchpath, if probed XXX.dylib and failed will attempt
XXX.so before moving to next path element (osx).

Package.searchpath, if probed XXX.dylib and failed will attempt
XXX.so before moving to next path element (osx).

Fixes #810