Chnages to image drawing

[Fred Kiefer]

I made some changes to the way an image gets drawn in xgps. Up to now
there was the official DPSimage method on XGContext (and a few similar
ones) that did not work at all and the function NSDrawBitmap that
worked, but ignored some of its arguments. This two mechanisms should
now both work the same, as I did extend the DPSimage method on XGGState
(And made its arguments more explicit, so that we can not mix up there
types any more, as it had been done). Functionally this should cause no
changes to any existing code, as the methods on XGContext where never
used and the additional transformation argument should in most cases be
the identity. Still I would like you all to test your favourite bitmap
application, if you see any changes and report them.
As soon as this small change is confirmed to work, I would like to get
the scaling on NSImageCell working. Which should now only require some
changes in gui.

Fred