Fix #439: socket must be closed on __gc

This patch also adds argument checking to all socket methods.
Remove broken struct sockaddr definition from FFI

Fixes compatibility with third-party modules.
Hide box.socket.internal
Merge branch 'stable'

Conflicts:
	src/lua/bsdsocket.cc
	src/lua/bsdsocket.lua
	test/box/bsdsocket.result
	test/box/bsdsocket.test
Change initialization order of socket module
Merge remote-tracking branch 'origin/master'