This commit adds the option to choose a movie clip in the camera settings, which will make Cycles
deform the rendered image according to the lens parameters of the clip.
This could already be done with the Movie Distortion node set to "Distort" in the Conmpositor,
but doing it directly in Cycles means that no unneccessary areas are rendered, areas that would
otherwise be outside of the frame are still rendered, there are no interpolation artifacts in the
result and the ray derivatives are correct.
Since LibMV can't be called from the kernel, the distortion model has to be inverted directly.
Blender only uses the radial distortion components, though, which means that simply inverting
the radius distortion using a few Newton iterations works well enough.