add a new function FrameSvg::alphaMask() that lets define an alpha-layer
for the frame, that can be the frame itself or a mask- prefix
allow for overlay elements on frames that can do a nice
filigrane-effect, they can either be:
-fixed position at 0,0
-random position consistent across plasma runs (only supported for applet
backgrounds)
-tiled
-scaled
svn path=/trunk/KDE/kdelibs/; revision=910655
