Sat Aug 21 16:53:17 BST 1999  Adam D. Moss  <adam@gimp.org>

	* plug-ins/common/jpeg.c:  Preview layers need to be alpha-padded,
	since they're not on the bottom of the stack.  That's a GIMP rule.

	Plus... use new API functions gimp_image_{freeze,thaw}_undo() to avoid
	the dilemma of either consuming a squillion superfluous tiles or
	clobbering the whole undo stack.

	* app/gimage.h
	* app/gimage_cmds.c
	* app/gimpimage.c
	* libgimp/gimp.h
	* libgimp/gimpimage.c: New API functions
	gimp_image_{freeze,thaw}_undo()	to avoid the above twin	evils.
	Similar to gimp_image_{disable,enable}_undo() but without
	clobbering the undo stack (I would have simply changed the latter,
	but too many plugins seem to rely on that behaviour).  See the PDB
	docs for slightly more information.