[ODE] Damping

[james at 6msoft.com]

> Furthermore applying velocity directly is less robust than applying a
> damping force directly.

Yeah, I understand that in many cases setting velocities directly is a bit
taboo, but in this case, all it would mean is it would become a function
of mass (which it really shouldn't be). I mean, I could do F=MA, but then
it would just turn around and do V=V+(dT*F/M), and seeing how worried
people are about the speed impact of clamping a floating point value, I
think I will try and save the CPU from factor then de-factoring mass. I
don't think we will be losing any robustness.

-James.