fix leak in Combo.
fix leak in Combo.

We leaked decorations, since UnDoLayout wasn't passed to the actual layouts
that had decorations attached.  :(

darcs-hash:20070616191052-72aca-9a2e2315e11257f5e5e35cd3944e2a4092919c74

jthornber/XMonadContrib,jthornber/XMonadContrib