Blender Git Loki

Tomato Cycles: internal cleanup of tile-based integrator

This commit solves couple of issues appeared with new integrator:

- Render job progress bar is now shows progress based on number of
rendered tiles. This is the same as Blender Internal does.

This still requires some further thoughts because for GPU it's
better to use single tile and in this case progress bar should
be based on number of rendered samples.

- Removes "global" sample counter from progress descriptor. There's
no more global-being sample which makes sense.

This counter was replaced with tile counter.

- Use proper sample number when copying render buffer to blender.
It used to be final sample number used which lead to tiles
appearing from complete dark to normal brightness as they're
being rendered. Now tile would be displayed with proper
brightness starting from the very first sample.

Use sample counter stored in render tile descriptor and pass
it to update / write callbacks.

This was tested on CPU and GPU CUDA rendering.

Additional change:

OpenCL rendering now should be cancellable before it finished
rendering all the samples (the same change as for CPU/CUDA from
a while ago).

This part of commit wasn't actually tested, would do it later.