The txn API must let the engine know when the first
statement happens in a multi-statement transaction.

For autocommit mode, statement transaction management
of read-only statements is just a thin layer around
fiber_gc().

Speed up txn construction and make txn object smaller:
* initialize triggers in txn on first use
* remove unnecessary members of txn
* replace rlist with slist (double linke list with single linke list)
  for statement list; implement a nicer single linked list for
  that purpose, and cover it with tests;

Streamline engine API:
* replace beginStatement with begin(),
  engines have no need to be alerted on each statement
* don't commit statement transaction inside the engine,
  do it once outside engine API
* TupleGuard -> TupleRef, implement TupleRefNil

Connection was declared successfully established prematurely; broke
tests on mac.

Conflicts:
	src/box/memtx_engine.cc
	src/lib/small

Accept all available sockets in accept callback.
This speeds up reconnection after restart.

Conflicts:
	src/evio.cc

Speed up acceptor with enabled io_collect_interval.

Fixed a bug in B-tree that could slightly break structure is presence of freezed iterators

box_introspection.rst -- some items in box.info() disappeared so their descriptions must also disappear

Event loop and garbage collecition make it extremely difficult
to maintain an easily cleanable state: if Lua is freed first,
some event cleanups may invoke Lua and crash. If events are
freed first, some Lua gc may invoke userdata destruction which
is pointing at event loop objects.

*)fixed gh-1070: upsert: use default tuple as the key
*)restored lost upsert tests

tests updated for new test-run
sophia_join.test.py implemented in lua

Voted by team