* clutter.symbols: Add ClutterBehaviourOpacity accessors.
* clutter/clutter-behaviour-opacity.h:
* clutter/clutter-behaviour-opacity.c:
(clutter_behaviour_opacity_set_bounds),
(clutter_behaviour_opacity_get_bounds): Add accessors for the
opacity-start and opacity-end properties.
* clutter/clutter-behaviour-scale.h: Fix the argument name to
avoid complaints by gtk-doc.