[Xmonad] darcs patch: catch exceptions when calling user-written code.

Note: this fixes issue 55. David Thu Oct 11 20:56:55 EDT 2007 David Roundy * catch exceptions when calling user-written code. Note: this is a less-than-minimal approach, since it seemed better to put the catchX in whenJust, rather than in both times whenJust is used in Main. As a result, it does a few potentially less efficient checks, but we're also slightly more robust with regard to bugs introduced in the future.