(get-conf-stat-older): Document the mask argument.
(mark-text-old): Document that mark-type 0 is used to remove the mark.
(async-leave-conf): This message is always sent to a person when
 	that person ceases to be a member of a conference, whatever the
 	reason is.  The protocol specification used to say that it was
	only sent when a person was forced to leave a conference.  The
	current wording makes more sense, and it was also the implemented
	behavior, so update the specification rather than the program.