[Xmonad] darcs patch: subLayouts for Combo (and 2 more)

This is a companion to the possibleLayouts removal patches. David, I'd like to know if serialization still works for Combo with these changes. Cheers, Spencer Janssen Thu Oct 4 15:09:48 CDT 2007 Spencer Janssen <sjanssen@cse.unl.edu> * subLayouts for Combo Thu Oct 4 15:11:35 CDT 2007 Spencer Janssen <sjanssen@cse.unl.edu> * subLayouts for LayoutModifier Thu Oct 4 15:26:10 CDT 2007 Spencer Janssen <sjanssen@cse.unl.edu> * Include subLayouts of ModifiedLayouts too