[Xmonad] BEWARE: restart/StackSet change

Due to recent StackSet changes restart (mod-q) probably won't work correctly after you pull and build this patch: Tue Jun 12 10:05:55 CDT 2007 David Roundy * make focus, up and down complete functions. This is a rerun of my change to make (Stack a) never be empty. Gives us more type-safety. After you've pulled this patch, build xmonad, put all your windows on the current workspace, then restart. Any windows that aren't currently visible will be lost. You only have to worry about this when upgrading from an old xmonad to the new version. Cheers, Spencer Janssen (this is a bug, I promise to fix it soon)