[Xmonad] darcs patch: make workspace tag not need to be a Num.

This is an amend-recorded version, which fixes a conflict with the recent haddock changes in StackSet. David Thu Jun 14 07:07:09 PDT 2007 David Roundy <droundy@darcs.net> * make workspace tag not need to be a Num. This change also removes the barely used 'size' field, and replaces it with a tagMember predicate. The idea is to move towards the ability to make the workspace tag be a String, which by default might be "1".."9", but could also be customized to be something meaningful to the user.