* Fractional frames support has been changed to use a new var, scene->r.subframe.
This is a 0.0-1.0 float representing a subframe interval, used in generating a final float
frame number to evaluate animation system etc.
* Changed frame_to_float() and some instances of bsystem_time() into a convenience function:
float BKE_curframe(scene) which retrieves the floating point current frame, after subframe
and frame length corrections.
* Removed blur_offs and field_offs globals. These are now stored in render, used to
generate a scene->r.subframe before render database processing.