Blender Git Loki

Cycles: add per object options to disable motion blur and set deformation motion steps.

Notes:

* The motion steps only affect deformation motion blur.
* The actual number of steps is 2^(steps - 1). This avoids having to sample at
many different times for object with more/fewer steps, now the times overlap.
* Deformation motion blur is enabled by default in existing files that have
motion blur enabled. If the object is not deforming, this will be detected at
export time, so raytracing performance will not be affected.

Part of the code is from the summer of code project by Gavin Howard.