actor: explicitly track children in clutter-actor.c
actor: explicitly track children in clutter-actor.c

We now explicitly track the list of children each actor has in a private
GList. This gives us a reliable way to know how many children an actor
has - even for composite actors that don't implement the container
interface. This also will allow us to directly traverse the scenegraph
in a more generalized fashion. Previously the scenegraph was
more-or-less represented implicitly according the implementation of
paint methods.

Distrotech/clutter,djdeath/clutter-multithreaded,GNOME/clutter,djdeath/clutter-android,nobled/clutter,collects/clutter,djdeath/clutter-multithreaded,heysion/clutter-clone,Distrotech/clutter,djdeath/clutter-multithreaded,djdeath/clutter,jigpu/clutter,collects/clutter,djdeath/clutter-android,collects/clutter,nobled/clutter,collects/clutter,heysion/clutter-clone,GNOME/clutter,djdeath/clutter,heysion/clutter-clone,jigpu/clutter,Distrotech/clutter,GNOME/clutter,djdeath/clutter-multithreaded,dlespiau/clutter,kerrickstaley/clutter-vala,collects/clutter,nobled/clutter,GNOME/clutter,ebassi/clutter,spatulasnout/clutter,djdeath/clutter,spatulasnout/clutter,djdeath/clutter,heysion/clutter-clone,ebassi/clutter,jigpu/clutter,ebassi/clutter,spatulasnout/clutter,spatulasnout/clutter,GNOME/clutter,djdeath/clutter-android,dlespiau/clutter,djdeath/clutter,djdeath/clutter-android,kerrickstaley/clutter-vala,jigpu/clutter,heysion/clutter-clone,spatulasnout/clutter,Distrotech/clutter,ebassi/clutter,jigpu/clutter,jigpu/clutter,djdeath/clutter-android,kerrickstaley/clutter-vala,Distrotech/clutter,kerrickstaley/clutter-vala,ebassi/clutter,dlespiau/clutter,Distrotech/clutter,djdeath/clutter