[ODE] Jitters

[Tyler Streeter]

> This gets at something I've been meaning to comment on for a while now.
> If you're doing damping by manually applying forces and torques, you really
> want them to be proportional to the body's *momentum*, not velocity.  Not
> only will this improving damping performance and stability over a wide
> range of object masses, but it will also prevent peculiar rotational motion
> that you might experience if you have bodies with peculiar inertia tensors.

Should the damping also be scaled by the simulation step size in this
case?  It seems important to factor in the step size if you're scaling
the velocity directly, but what about the cases where you're adding an
opposing force/torque proportional to eithe velocity or momentum?

Tyler