owl_util_file_delete_line in perl
Add a ~/.owl/ircchannels file, persist channels

All irc channel subscriptions persist across reconnects.

irc-{part,join} now have a -t flag, which makes the channels not persist
across BarnOwl sessions.

irc-loadchannels loads persistent channels.  It does not unload existing
channels.
Update completion for :irc-{join,part}