[xmonad] bringing xmonad into the threaded world

There have been various times when I've wished I could just spawn a thread in xmonad. Just recently, for example, it was pointed out to me that the default mod+q binding starts a brand new process just to keep xmonad responsive while it recompiles the configuration file. This is silly. Here is a patch bundle that makes xmonad ask X to be thread-safe, and rewrites the default mod+q binding to take advantage of the new thread safety. ~d