Blender Git Loki

Cycles: Fallback to bottom-top tile order when rendering from the command line

In the worst case it'll do nothing, in the best case it might give some percent
of speedup because of better cache coherency.

Currently it's all handled as an override on blender_python level, don't really
see reason to penetrate the boolean flag further into sync code. This can always
be done later if needed.