2006-11-09  Michael Natterer  <mitch@gimp.org>

	Properly abstract brush scaling:

	* app/core/gimpbrush.[ch]: added virtual functions
	GimpBrush::scale_mask() and ::scale_pixmap() and default
	implementations which call the functions in base/brush-scale.c.

	* app/core/gimpbrushgenerated.c: factored out brush calculation to
	an internal utility function and call that function from ::dirty()
	and from the new ::scale_mask().

	* app/core/gimpbrushcore.c: use gimp_brush_scale_mask/pixmap()
	instead of using the lowlevel scale functions directly. Fixes the
	uglyness that we were scaling generated brushes instead of simply
	recalculating them in the right size.