Blender Git Loki

Depsgraph/Python: callbacks and properties to detect datablock changes

* Adds two new python handlers: scene_update_pre() and scene_update_post()
These run before and after Blender does a scene update on making modifications
to the scene.
* Datablocks now have an is_updated property. This will be set to true in the
above callbacks if the datablock was tagged to be updated. This works for the
most common datablocks used for rendering: object, material, world, lamsp,
texture, mesh, curve.
* Datablock collections also have an is_updated property. If this is set, it
means one datablock of this type was added, removed or modified. It's also
useful as a quick check to avoid looping over all datablocks.
* RenderEngine.view_update() can also check these properties, for interactive
viewport rendering.

http://wiki.blender.org/index.php/Dev:2.6/Source/Render/UpdateAPI