Commit patch #7788, allow to set the render step, so it's
possible make render every N frames only.
The step is change in Scene buttons (F10), below start and
end frame buttons.
Also add a command line options (-j), so it's possible to
overwrite the file step (useful for renderfarm).
[ Brecht, this work with OpenGL renders and simulated
the skipped frames, please double check ]
4f737bafa7