* dbus/dbus-transport-unix.c (do_authentication): Return
	authentication status to callers.
	(unix_handle_watch): If we completed authentication this round,
	don't do another read.  Instead wait until the next iteration,
	after we've read any pending data in the auth buffer.
	(unix_do_iteration): Ditto.
	(unix_handle_watch): Updated for new do_authentication prototype.