update the slack mark on irssi mark command or window change/activity
update the slack mark when we're at the bottom and new messages are received
only update the slack mark on new public messages for the active window
mark any windows that were requested
mark some variables as local
'window activity' isn't what we want; 'message public' seems to be enough
Merge pull request #1 from jwm/jwm_update_slack_mark

update the slack mark on irssi mark command or window change/activity