[ODE] fixed time steps

[Morgan McGuire]

If you use code like this:

> #define FIXEDSTEP 0.006
> float curTime;
> void StepODE (float dtime)
> {
>   static float lastTime = 0;
>   curTime += dtime;
>   loops=0;
>   while(lastTime<curTime){
>     lastTime += FIXEDSTEP;
>     dSpaceCollide(space, 0, &nearCallback);
>     dWorldQuickStep(world, FIXEDSTEP);
>     dJointGroupEmpty(contactgroup);
>   }
>}

I believe you will end up zeroing your force accumulators after the 1st iteration and produce incorrect results.  You have to run all of your own simulation code after dWorldQuickStep inside the loop.  (Please correct me if I'm wrong!)

-m