pull suppressWhen logic into main WithUrgencyHook handler
pull suppressWhen logic into main WithUrgencyHook handler

In order for this to work, I added a new UrgencyHook method to communicate the
SuppressWhen value. I'm not sure if this is actually better than just providing
a convenience function, but it's an easy switch.

darcs-hash:20080513075247-78224-760cd588622855d35f7acaae1084396f38b7b634

jthornber/XMonadContrib,jthornber/XMonadContrib