Build Sophia before trying to link with it.

Conflicts:
	src/box/memtx_hash.cc
	test/unit/CMakeLists.txt

Conflicts:
	test/box/box.net.box.result

set_snapshot_lsn is called at server start,
and snapshot() API is used to save a snapshot.

Conflicts:
	src/box/box.cc
	src/box/engine.cc
	src/box/recovery.cc
	src/box/recovery.h

Now wal_watcher can be used in a threaded context, make it a
member of struct recovery.
Begin changing recover_remaining_wals to use exceptions.

Cover mistakes found while implementing
https://github.com/ziontab/lua-nginx-tarantool

Regression introduced by 1376aad9

Add a new IPROTO request type - EVAL. EVAL compiles and executes arbitrary
Lua expression and returns raw result (without converting it to a list
of tuples).