2003-05-18  Michael Natterer  <mitch@gimp.org>

	Implemented "Flip Image". Fixes bug #23179:

	* app/core/core-enums.[ch]: added GIMP_UNDO_GROUP_IMAGE_FLIP.

	* app/core/Makefile.am
	* app/core/gimpimage-flip.[ch]: new files implementing
	gimp_image_flip().

	* app/gui/image-menu.c
	* app/gui/image-commands.[ch]: added it to the "Image" menu.

	* themes/Default/images/Makefile.am
	* themes/Default/images/stock-flip-horizontal-16.png
	* themes/Default/images/stock-flip-vertical-16.png
	* libgimpwidgets/gimpstock.[ch]: added icons for the new
	menu items.

	Bugs found while hacking the stuff above:

	* app/core/gimpdrawable-transform.c (gimp_drawable_transform_paste):
	only call gimp_layer_add_alpha() if the pasted tiles have alpha.

	* app/core/gimpimage-undo-push.c (undo_pop_channel_mod): fixed to
	do the right thing if the channel is the selection mask.