A problem happens when clip->all_clipped is set and we go to get a clipped
context. Normally backends don't see operations with clip->all_clipped and so
_cairo_surface_clipper_set_clip is designed with the assumption that
clip->all_clipped is never true. I added a work-around by manually setting the
CGContextClip with an empty rectangle, however this caused cairo to be confused
about what the actual clip was.
This patch fixes the problem by adding a new function
cairo_quartz_finish_cg_context_with_clip that is called after we're done with
the native context. It moves the CGContextSave/RestoreGState calls out of
gfxNativeDrawing into cairo and uses them to ensure that the clip remains
consistent with cairo's model of them.
