* make sure long-run tests pass
* more systematic approach to downcasts to MemtxIndex in
alter/system spaces code

Support multi-part keys. Allow key duplicate
compaction. Reduce storage cost, encode metadata,
do not store msgpack (except value part).
Reconstruct tuple on read using index schema.

[replication]

JOIN support temporary put to not working
condition: there is no way to access possibly
deleted space schema during the operation
for a tuple reconstruction
(multi-thread).

recreate space key_def during join; enable join

sophia: make every operation asynchronous

sophia: fix join cursor and tests

sophia: implement delayed update operation

sophia: make delete write-only

implement Handler::executeReplace

sophia: merge fixes

make upsert operation an engine specific

sophia: make update logic common to memtx

sophia-integration: switch to Sophia v1.2.3; implement upsert

sophia: add half_commit mode support

This mode disables conflict resolution for
'prepared' transactions and solves the issue with
concurrent write-write conflicts during wal write/yield.

sophia: do not allocate tuple during replace or update; refactoring

sophia: extend and reorganize test suite

sophia: implement box.sophia()

sophia: #681: support or produce error on space::alter

sophia: extend recover tests

sophia: add separate iterator tests

box: enable per-engine select

    * add executeSelect() into engine handler API
    * add MemtxIndex; move preallocated m_position from Index to MemtxIndex
    * remove it->close()
    * remove IteratorGuard class

    note: Sysview and Sophia engines yet share the same select code in
    engine::executeSelect() (which does iterator alloc-free)

box: remove close call from box_iterator_free()

finalizers.test marked as long run in suite

 *) added stress test for snapshotting
 *) moved finalizers.test.py to long_run

* Fix gh-698: duplicate-key error followed by segfault

* Add long_run test suite, which include test case from the
ticket for memtx and sophia engines.
Result files must be zero-diff

Test script also has been fixed in a number of ways:
  a) crud operation on sophia space always return nil
  b) sophia_space:len() is not monotonous
  c) update of primary key is not allowed

* Fix return of vclock_sum() as wal_writer() result, reuse
it for txn->signature

* Fixed incorrect tuple guard usage in execute_delete()

* Fixed sophia delete operation: return old_tuple as an
exception for SophiaIndex::replace(). Do not skip
wal_write() and correctly set txn->signature

* Put engine commit code after wal_write(), reuse proper
txn->signature. Engine->commit yet can throw an exception
on concurrent transaction conflict or error

* rollback sophia transaction on conflict

* add second test for gh-698; rename and disable zlong_run tests

* make rollback statement engine specific

* make txn_finish() engine specific; use it both by commit/rollback to gc

* refactor execute_delete()

* upgrade sophia submodule: efficient msgpack storage

* engine api: style fixes