Internet Relay Chat (IRC) is handled by handing off
the irc session to a function named in
url-irc-function.
A function to actually open an IRC connection. This function must take five arguments, host, port, channel, user and password. The channel argument specifies the channel to join immediately, this can be
nil. By default this isurl-irc-rcirc.
Processes the arguments and lets
rcirchandle the session.