Try to handle concurrent close on socket more gracefully

Try to handle concurrent close on socket more gracefully

	* fhandler_socket.cc (LOCK_EVENTS): Don't enter critical section with
	invalid mutex handle since then socket has been closed.
	(UNLOCK_EVENTS): Close critical section.
	(fhandler_socket::evaluate_events): Handle calling connect on shutdown
	socket.
	(fhandler_socket::wait_for_events): Try for pthread_testcancel in case
	of WAIT_FAILED.  Try to come up with a better errno in case we waited
	on an invalid handle.
	(fhandler_socket::release_events): Change wsock_mtx and wsock_evt to
	NULL under lock to avoid accessing invalid handle.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>