2000-12-15  Sven Neumann  <sven@gimp.org>

	* app/gimppreviewcache.[ch]: added new function gimp_preview_scale().

	* app/channel.c
	* app/channels_dialog.c
	* app/gimpimage.c
	* app/layer.c
	* app/layers_dialog.c
	* app/lc_dialog.c
	* app/nav_window.c: unified preview drawing code. Previews are never
	generated larger than the canvas size. Image and channel previews are
	scaled up to the desired size, so does the navigation window. The
	layer previews are not yet scaled up again since we can not use
	gimp_preview_scale here. I have removed the preview_cache priming
	code since we don't need it any longer and it caused bad results.