2004-03-13  Sven Neumann  <sven@gimp.org>

	* app/core/gimpdrawable.[ch]: added new virtual function
	GimpDrawable::set_tiles().

	* app/core/gimpchannel.c
	* app/core/gimplayer.c: push an undo before chaining up in
	set_tiles().

	* app/core/gimpdrawable-transform.c
	* app/core/gimpimage-convert.c
	* app/tools/gimptransformtool.c: use gimp_drawable_set_tiles()
	instead of fiddling with the drawable's tile manager directly.