This patch also fixes incorrect offset calculation in buffer
with multiple responses:

    self.rbuf = string.sub(self.rbuf, off + 1)

Box still have a global pointer to its recovery state.
This pointer must only be used from TX thread from main process.

This patch is pre-requisite for thread-based JOIN/SUBSCRIBE handlers.

Other changes:

 * Add box_atfork() and recovery_atfork() callbacks
 * Change signature of recovery_state->row_handler
 * Execute JOIN request via box
 * Remove r->join_handler callback from recovery subsystem

`_func' space recovered before `_user' and auth_token can't
be retrived during creating struct func_def.

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

Extract the non-failing parts of the original patch by Roman.
Make an attempt at finding why coeio_custom is crashing when
replication_source is changed quickly - no success yet.

Recognize -w --wrapper, and don't daemonize if run from a wrapper.