2003-09-03  Michael Natterer  <mitch@gimp.org>

	* app/core/gimpchannel.[ch]: made all functions which push an
	undo step virtual and added them all as default implementations.

	* app/core/Makefile.am
	* app/core/core-types.h
	* app/core/gimpselection.[ch]: new object which is a GimpChannel
	subclass and implements all of its virtual functions, pushes
	an image_mask undo and chains up with "push_undo = FALSE".

	* app/core/gimpimage-mask.[ch]: made most functions simple
	wrappers like gimp_channel_invert(gimp_image_get_mask(gimage));
	so the API stays the same for now.

	* app/core/gimpimage.[ch]: create a GimpSelection object
	as gimage->selection_mask. Removed "gboolean mask_stroking"
	since it is in GimpSelection now.

	* app/xcf/xcf-load.c (xcf_load_channel_props): added an evil hack
	which turns a GimpChannel into a GimpSelection once we figured the
	loaded channel is the selection.

	* app/core/gimplayer.c (gimp_layer_create_mask):
	gimp_channel_clear() takes an additional "const gchar *undo_desc"
	parameter now.

	* app/core/gimpscanconvert.c (gimp_scan_convert_to_channel): set
	mask->bounds_known to FALSE before returning the new channel

	* app/tools/gimpiscissorstool.c (iscissors_convert): no need to
	call gimp_channel_invalidate_boundary() on the channel returned by
	the above function.

	* app/core/gimpchannel.[ch]: removed
	gimp_channel_invalidate_boundary() since it is no longer needed.