(rcirc-ignore-list-automatic): New variable.
(rcirc-print): Take rcirc-ignore-list into account.
(rcirc-cmd-ignore): New command.
(rcirc-ignore-update-automatic): New function.
(rcirc-handler-PART, rcirc-handler-QUIT): Use it to maintain the
list if ignored nicks.
(rcirc-handler-NICK): Ditto, and also ignore the new nick.