fix leak in Combo.
fix leak in Combo.

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

f1u77y/xmonad-contrib,0/xmonad-contrib,0/xmonad-contrib,mathstuf/xmonad-contrib,CaptainPatate/xmonad-contrib,xmonad/xmonad-contrib,ohlus/xmonad-contrib,CaptainPatate/xmonad-contrib,ohlus/xmonad-contrib,CaptainPatate/xmonad-contrib,xmonad/xmonad-contrib,ohlus/xmonad-contrib,0/xmonad-contrib,f1u77y/xmonad-contrib,pjones/xmonad-test,mathstuf/xmonad-contrib,mathstuf/xmonad-contrib