[ODE] Locators - Center of mass

[Geoff Carlton]

Remi Ricard wrote:
>
> Talking about the memory used. There should be no change since dMass 
> has already the position of the center of mass.
> We should just use it.
>
I think that there would be a bit more overhead than that, unless the 
solvers were modified to use the mass's offset directly.  But that is 
just a guess, if you look at it you might come up with a solution that 
makes everybody happy!

Geoff