2002-01-31  Michael Natterer  <mitch@gimp.org>

	* app/core/gimplayer.[ch]: removed gimp_layer_has_alpha(), use
	gimp_drawable_has_alpha() instead.

	* app/core/gimpimage-convert.c
	* app/core/gimpimage-merge.c
	* app/core/gimpimage-projection.c
	* app/display/gimpdisplayshell.c
	* app/gui/layers-commands.c: changed accordingly.

	* app/core/gimpimage.[ch]: added gimp_image_has_alphe(), made some
	variable names more verbose and use enum types instead of "gint"
	in functions calling initial_region() and combine_regions().

	* app/widgets/gimpchannellistview.c: show an alpha channel preview
	only if the image has alpha.

	* app/widgets/gimppreview.c: reordered functions,
	gimp_preview_render_and_flush(): fixed channel preview rendering,
	calculate the component byte offsets before entering the render
	loop instead of duplicating the render code for the gray/alpha
	case.