* app/drawable_cmds.c, app/gimage_cmds.c
	* app/parasite_cmds.c, libgimp/parasite.[ch],
	* libgimp/gimp.c, libgimp/gimpprotocol.c
	* tiff.c, gif.c, script-fu.c: removed all references to
 	parasite_error() and parasite_is_error().  Enable the
	passing of null parasites in the pdb.  Return a copy of the
	parasite instead of the orginal in all pdb functions.