2004-04-19  Sven Neumann  <sven@gimp.org>

	* app/widgets/gimpenumstore.[ch]: avoid unnecessary casts.

	* app/widgets/gimpenumcombobox.[ch]: added an API that inserts a
	GtkTreeModelFilter to make items invisible. This is a kludge to
	workaround bug #135875.

	* app/tools/gimpcurvestool.c
	* app/tools/gimplevelstool.c
	* app/widgets/gimphistogrameditor.c: use the new function to hide
	histogram channels that are not available with the current
	drawable.