New #:right option for wm.tile.tall/tall-tiling

New keyword parameter for sawfish.wm.tile.tall/tall-tiling to place
the main window to the right (instead of to the left) side.
New #:master predicate for wm.tile.tall/tall-tiling

One can now specify a predicate that will be used to select which
window(s) can occupay the master pane in tall tilings.