Remove unused constant flood_protection

Was not used and user can set flood_interval to 0 to acheive the
intended result.
Fix up flood_check()

Very clunky and not working before, can be a lot smoother.
Make variable/function/constant style consistant

Not saying mine are better than yours, just they should all match
each other.
Show the 2nd party that the 1st party was notified

via a short /me message.
Only skip for current buffer if FORCE_ENABLED on

People without FORCE_ENABLED are using /away and will want
notification in the current window.

also change types of FORCE_ENABLED and FLOOD_INTERVAL, strings are
a daft idea for thse.
quick bugfix wrt scope of old_time