2004-09-29  Sven Neumann  <sven@gimp.org>

	* libgimpwidgets/gimppreview.[ch]
	* libgimpwidgets/gimpwidgets.def: added gimp_preview_draw_buffer().

	* libgimp/gimpaspectpreview.[ch]
	* libgimp/gimpdrawablepreview.[ch]
	* libgimp/gimpui.def: removed the public draw_buffer API.
	Implement the virtual GimpPreview::draw_buffer method instead.

	* plug-ins/common/cartoon.c
	* plug-ins/common/deinterlace.c
	* plug-ins/common/despeckle.c
	* plug-ins/common/dog.c
	* plug-ins/common/edge.c
	* plug-ins/common/engrave.c
	* plug-ins/common/exchange.c
	* plug-ins/common/gauss.c
	* plug-ins/common/grid.c
	* plug-ins/common/neon.c
	* plug-ins/common/noisify.c
	* plug-ins/common/oilify.c
	* plug-ins/common/photocopy.c
	* plug-ins/common/plasma.c
	* plug-ins/common/sel_gauss.c
	* plug-ins/common/sharpen.c
	* plug-ins/common/shift.c
	* plug-ins/common/snoise.c
	* plug-ins/common/sobel.c
	* plug-ins/common/spread.c
	* plug-ins/common/struc.c: changed accordingly. Don't pass the
	preview around as GimpDrawablePreview or GimpAspectPreview. It
	should whenever possible be accessed as GimpPreview.