Remove CheckBuiltInFunctionExists logic from CMake
Add an error message about GCC 4.7 and libobjc2 to CMake
Fix warnings detected by clang
Fix ObjC Clang build broken by 13054aaa46d3c1db7263c449d085c87156fd86ea
Merge remote-tracking branch 'origin/stable' into stable
Merge branch 'stable'

Conflicts:
	cmake/compiler.cmake
	include/sio.h
	src/box/bitset_index.cc
	src/box/box_lua.cc
	src/lua/init.cc
	src/lua/session.cc
	src/sio.cc
	test/unit/objc_catchcxx.m
	third_party/luajit