add reminder functionality to UrgencyHook
add reminder functionality to UrgencyHook

I'm considering rewriting remindWhen and suppressWhen as UrgencyHookModifiers, so to speak. Bleh.

darcs-hash:20080824200548-78224-8589b08cc15bcb9506c0e86df832c1d7a73efaa8

kmels/xmonad-launcher,kmels/xmonad-launcher