* app/actions/tools-actions.c
	* app/actions/tools-commands.[ch]: add new actions for
	toggling "fixed-aspect" and "fixed-center" options of
	rectangle tools.

	* app/tools/gimprectangletool.[ch]
	* app/tools/gimprectangleselecttool.c
	* app/tools/gimpcroptool.c: rely on new actions for
	keyboard control, not on modifiers pressed after
	mouse1-down.