2002-06-06  Michael Natterer  <mitch@gimp.org>

	* app/core/gimpchannel.[ch] (gimp_channel_invert): added a boolean
	"push_undo" parameter.

	* app/core/gimpimage-mask.c
	* app/core/gimpimage-qmask.c: pass push_undo == TRUE.

	* app/core/gimplayer.c (gimp_layer_create_mask): call
	gimp_channel_invert(), not gimp_drawable_invert() because the
	latter takes the current selection into accout (reported by Jimmac
	on #gimp). Added g_return_if_fail() stuff to all public functions.
	Cleanup.