[xmonad] [patch] Selective modifier

Hi This patch adds a layout modifier which limits the number of windows visible, but in a "smarter" (and possibly more useful) way than the LimitWindows modifiers. It displays the first nMaster windows (in my use this corresponds to the master pane of Tall) and nRest other windows, in such a way that the focussed window is always visible, but if focus moves to another visible window then nothing moves. It should be merged into LimitWindows, but I'm putting it out there. I'll eventually merge it myself, if nobody else does. Cheers, Max