Blender Git Loki

Cycles: Solve possible issues with running out of stack memory allocator

Policy here is a bit more complicated, if tree becomes too deep we're
forced to create a leaf node and size of that leaf wouldn't be so well
predicted, which means it's quite tricky to use single stack array for
that.

Made it more official feature that StackAllocator will fall-back to
heap when running out of stack memory.

It's still much better than always using heap allocator.