2004-05-13  Michael Natterer  <mitch@gimp.org>

	Added GimpViewable infrastructure which enables migrating from
	TempBuf to GdkPixbuf for both providing and getting previews:

	* app/core/gimpviewable.[ch]: added new virtual functions
	GimpViewable::get_pixbuf() and GimpViewable::get_new_pixbuf()
	which are implemented exactly as get_preview() and
	get_new_preview() except that get_new_pixbuf() has a default
	implementation which creates the pixbuf from a TempBuf.

	Renamed public functions _get_preview_pixbuf() and
	_get_new_preview_pixbuf() to _get_pixbuf() and _get_new_pixbuf().

	Added gimp_viewable_get_dummy_pixbuf() and use it from
	gimp_viewable_get_dummy_preview().

	* app/core/gimpimagefile.c (gimp_imagefile_save_thumb)
	* app/display/gimpdisplayshell.c (gimp_display_shell_update_icon)
	* app/gui/resize-dialog.c (resize_dialog_new): changed accordingly.