Blender Git Loki

Bugfix #4561

Sequence renders, calling scenes with compositing, didn't execute composite
correctly. Confusement caused by the rule that a "Render" handle has same
name as Scene, which gives conflict for the case when a Scene has
sequencing with Scene strips with its own scene in it.

The previous solution for that conflict caused composite not to work. This
commit solves that, but it is still hackish. Main reason is the still
bad global G.scene, in use by compositor.