MSScrollCut On/Off ; 0=Paste stencil/cookie, <>0=Cut using stencil/cookie

Sets the `cut' mode of the MSScroll family of scroll's On or Off. If On, any
calls the Stencil-Scrolls will cause the source image to be placed behind the
stencil or cookie protected areas of the destination. If SScrollCut is switched
off it will cause the Stencil-Scrolls to perform the same operation on the
stencils and cookies as is performed on the images and no cutting/protecting will
be performed, which corresponds to a normal `SBlit'.