drawing (to support transparency without overlay hacks and blend in notes
and other stuff). I'm sure this can be simplified a lot, but I can't see
how to cut code now. ThumbnailList still has the old code.
Now we have no wasted repaints. Also per-page allocated memory is less. Now
we need more repaints, since the viewport gfx looks broken. I hope not to
revert this, but find a unique short way to describe composted gfx ops.
Note: there is a swith in config to switch between plain and composted
rendering engines.

svn path=/branches/kpdf_experiments/kdegraphics/kpdf/; revision=359096