MSG_EXIT can now have a return code in the message, so check for that size as well. Stops the client fatal()ing on exit.
MSG_EXIT can now have a return code in the message, so check for that
size as well. Stops the client fatal()ing on exit.

klaxalk/tmux,klaxalk/tmux,klaxalk/tmux,klaxalk/tmux,klaxalk/tmux