Avoid clutter segfaulting when used without invoking
clutter_init(). This is needed when using api documentation
tools and every other tool relying on the GObject
introspection API (esp. on a headless box). see the
note in clutter/clutter-feature.c:clutter_feature_init
for a full explanation.
* clutter/clutter-feature.c: Call clutter_feature_init()
when needed by one of the accessors of the features
structure.
* clutter/clutter-main.c:
* clutter/clutter-private.h: Remove clutter_feature_init()
public declaration: the features support check is done the
first time a feature is needed.
* clutter/clutter-main.c: Do not ever access the clutter
main context pointer directly; instead, obtain a pointer
to it via clutter_context_get_default(), which will always
return something valid.
* clutter/clutter-behaviour-path.h:
* clutter/clutter-behaviour-path.c: Add a "knot-reached" signal,
which is emitted when the path reaches a node in the nodes list;
flesh out the documentation a bit; sync the parameters names
so that gtk-doc doesn't complain about missing stuff.
* clutter/clutter-behaviour.h:
* clutter/clutter-behaviour.c: Add the alpha value to the
ClutterBehaviour::alpha_notify vfunc, so you don't have to
get the value from the alpha inside the behaviour implementations;
add more documentation.
* clutter/clutter-alpha.c: Flesh out the description.
* clutter/clutter-actor.h: Update the header.
* clutter/clutter-behaviour-opacity.c:
* clutter/clutter-behaviour-scale.c: Update docs.
