[Xmonad] darcs patch: make quickcheck tests friendlier to read.

Hi all, This is just a silly patch to make it easier to deal with failed quickcheck properties in ghci. Derives a read instance for StackSet, and makes windows T be Char, so they're easier to distinguish when a StackSet is printed. David Sat May 5 10:54:15 PDT 2007 David Roundy * make quickcheck tests friendlier to read.