Add ifWindow and ifWindows and simplify WindowGo
Add ifWindow and ifWindows and simplify WindowGo

Ignore-this: 4ed6e789034db8804accfe06a47ef4a2

This patch adds ifWindow and ifWindows as helper functions to
X.A.WindowGo and removes some boilerplate by rewriting other functions
in terms of those. Also some minor simplifications.

darcs-hash:20090624231711-7f603-4c0bf4bc2542fe591ddeab25e21f4dd7a775afa7

yzhou61/xmonad-contrib,yzhou61/xmonad-contrib,yzhou61/xmonad-contrib