closes #541

Merge branch 'stable'

Conflicts:
	test/box/bsdsocket.test

Conflicts:
	src/lua/bsdsocket.lua
	test/box/bsdsocket.result
	test/box/bsdsocket.test

A dropped user structure could still be accessed from sessions
which were authenticated with this user.

Check that a user is dropped when accessing it from the authenticated
session.

 + Add tarantoolctl enter instance_name command

This patch also changes box.info.server output for this case.

Avoid uncontrolled growth of region memory.

Stop producing "excessively sparse array"

Other changes:

 - "" or NULL=ffi.cast('void *', 0) now resets option to default value
 - app/cfg.test.lua converted to TAP format

Tarantool started to use getaddrinfo() to find suitable address for
binding both for IPROTO and CONSOLE ports. A hostname can be resolved to
various addresses families, depending on user settings. For example, all
moderns systems resolve 'localhost' to '::1' by default. This creates a
problem if one subsystem binds to '127.0.0.1' and some other tries to
connect '::1'. This patch unify hardcoded names and addresses in entire test
suite to use the same value. This is pre-requisite for #447, #368 and other
URI-related patches.

Other changes:

  * console.listen() now properly handles address arguments
  * console.listen() re-based on socket.tcp_server() code