[Xmonad] darcs patch: Fix bug in noDuplicate invariant

[Donald Bruce Stewart]

bobstopper:
> Fri May 25 15:08:42 JST 2007  Rob <bobstopper at bobturf.org>
>   * Fix bug in noDuplicate invariant
>   ws used by noDuplicates is actually a list of list of elements which 
>   will pretty rarely raise any flags even if the StackSet actually does
>   contain duplicates. This patch concatenates ws to ensure the quickcheck
>   property tests accurately.


Applied.

-- Don