2006-10-25  Michael Natterer  <mitch@gimp.org>

	Added mechanism that should prevent undo corruption by
	broken plug-ins and scripts. Work in progress.

	* app/plug-in/Makefile.am
	* app/plug-in/gimpplugin-cleanup.[ch]: new files that (for now)
	keep track of the undo groups plug-in procedures open and close,
	and can fix an image's undo group state after a plug-in messed.

	* app/plug-in/gimppluginprocframe.h (struct GimpPlugInProcFrame):
	keep a list of plug-in cleanup structs.

	* app/plug-in/gimppluginprocframe.c
	(gimp_plug_in_proc_frame_dispose): call gimp_plug_in_cleanup() if
	the list is not empty.

	* tools/pdbgen/pdb/undo.pdb: keep track of undo groups using
	the new gimp_plug_in_cleanup_undo_group_start() and _end()
	functions. Fail if any of the functions returns FALSE.

	* app/pdb/undo_cmds.c: regenerated.