bind protocol-specific commands. Added #define command_bind_irc() for easier
access. CMD_IRC_SERVER(server) check should be done at the beginning of each
command requiring IRC server as active server, it handles it correctly the
cases when it is not. Did some other cleanups as well.
git-svn-id: http://svn.irssi.org/repos/irssi/trunk@1955 dbcabf3a-b0e7-0310-adc4-f8d773084564
