[Xmonad] darcs patch: simplify StackSet.delete (and 2 more)

Sorry, I forgot to send this earlier. These are the changes needed to support sticky windows. David Sun Jun 24 07:48:54 PDT 2007 David Roundy * simplify StackSet.delete Sun Jun 24 07:59:31 PDT 2007 David Roundy * make delete work when window is in multiple workspaces. Sun Jun 24 08:02:08 PDT 2007 David Roundy * fix apparent memory leak when floating windows are deleted.