2004-03-15  Michael Natterer  <mitch@gimp.org>

	Closer to text layer undo:

	* app/core/gimpchannel.c (gimp_channel_set_tiles): invalidate the
	channel's boundary and bounds.

	* app/text/gimptextlayer.c: implement GimpDrawable::swap_pixels()
	and set text_layer->modified = TRUE after upchaining.

	(gimp_text_layer_render): use gimp_drawable_set_tiles() and
	set text_layer->modified = FALSE afterwards.

	* app/core/gimpimage-undo-push.c: cleaned up variable declarations
	and initializations.

	(undo_pop_layer_mod)
	(undo_pop_channel_mod): use gimp_channel_set_tiles() instead of
	touching drawable->tiles manually. Now all pixel manipulation
	(at least on layers) should be virtualized and can be detected by
	the text layer.