[xmonad] darcs patch: X.U.WindowProperties, add getProp32 and getProp32s, helper functions to get window properties

This patch adds two helper functions to WindowProperties, getProp32 and getProp32s, to get window properties from atom and string respectively. This is a more generic implementation from the ManageDocks getProp code, this patch makes that module use this functions, and the ManageHelpers module too. Hope it's good, bye!