slab_arena allows to have multiple allocation
sources of differnt type for different purposes.
E.g. one can have MAP_PRIVATE arena for runtime
memory and MAP_SHARED for tuples.

The arena can be shared across multiple threads.
Implement such arena, cover with tests, use
it for region allocators.

Conflicts:
	CMakeLists.txt

Conflicts:
	src/CMakeLists.txt
	src/box/box_lua.cc
	src/lua/session.cc

The patch should use struct session, which is non-existent
in 1.5, so at least make session_storage_destroy a bit faster.

Conflicts:
	include/tarantool.h
	src/box/box.cc
	src/replica.cc
	src/replication.cc

Conflicts:
	src/admin.cc
	src/admin.rl
	src/box/bitset_index.cc
	src/box/hash_index.cc
	src/box/hash_index.h
	src/box/space.cc
	src/box/space.h
	test/box/admin.result

This patch implements show index and shows memory waste of the
slab allocator.

Conflicts:
	doc/user/configuration-reference.xml
	doc/user/persistence-architecture.xml
	doc/user/stored-procedures.xml

Conflicts:
	test/lib/tarantool_server.py
	test/lib/test_suite.py
	test/lib/unittest_server.py

misc cleanup

Because of v2->v3 migration mess different systems have different python
set by default. It is recommended to use versioned binaries.

Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>

Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>

Fixes gh-153.

-related distributions due to libbfd crash