Fix a subtle bug with blocked event loop when joining checkpoint thread.
Celeanup included headers in memtx_engine.cc

Implement a cap on the size of the worker fiber pool in iproto (1024
fibers by default).
Don't maintain too many fibers in the fiber cache of iproto.

Correct the assertion to match the logic of the code.

Conflicts:
	doc/sphinx/book/box/box_introspection.rst

Chagne iobuf to use slab_cache directly, bypassing an intermediate
allocation layer - this is necessry to make iobuf multi-threading
safe.

Introduce mpstream API to lua-msgpack encoder, which allows it
to encode msgpack into any memory source. The streaming API
should make it possible to encode even directly to network.

Patch region allocator to support the new API.
Patch iobuf/obuf output buffer of iproto to support the new API.

Extract Exception::clear(), Exception::move(), fiber()->exception
into struct diag methods. This refactoring makes desired logic
to be more clear.

Conflicts:
	src/iproto_port.cc

*) fixed potentionally unsafe code:
  on memory fail there could be port->found > 0 and uninitialized port->svp

 on memory fail there could be port->reply.found > 0 and uninitialized port->svp,
 that could lead to random error after svp restoration.
*) possibly fixed OPENTAR-97

finalizers.test marked as long run in suite

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

test-run udpated

set test-run module in gh-3 branch for review

closes gh-856

Conflicts:
	include/fiber.h
	include/mutex.h
	src/admin.cc
	src/admin.rl
	src/box/box_lua.cc
	src/box/request.cc
	src/box/txn.cc
	src/coeio.cc
	src/coio.cc
	src/fiber.cc
	src/ipc.cc
	src/iproto.cc
	src/log_io.cc
	src/lua/bsdsocket.cc
	src/lua/init.cc
	src/lua/session.cc
	src/memcached-grammar.cc
	src/memcached-grammar.rl
	src/memcached.cc
	src/recovery.cc
	src/replica.cc
	src/replication.cc
	src/say.cc
	src/session.cc
	src/tarantool.cc
	src/util.cc