[ODE] C++

[Colin Reed]

> hmmmm, i remember not implementing this because i didn't think it
> would be useful. i'll add this for the next release.
> what do you need this fn for? (just interested).

:-) When implementing springs, I first find the world position of each
of the ends of the spring and then find the velocity of these points in
order to find the relative velocity, I guess I could just find the
velocity of the body relative point, so this function is not actually
NEEDED.

Colin