[ODE] Boxiangle collision

[Chris Campbell]

> vertex data out of Demeter.  Have you compared your approach 
> against his
> for CPU or memory efficiency?

No I haven't. I think CPU efficiency is not too bad but memory like I said
('I will eventually need to do it some other way') will be an issue if you
intend to make a lot of these. Actually another issue is this, which I still
haven't figured out:

1) The sphere falls in a 'valley' between two triangles, so we should really
add them both as contacts in order to get the best reaction direction ->
shouldn't ignore multiple contacts.
2) The sphere falls on a perfectly flat heightmap, close to the edge between
two triangles. If the sphere is low enough, it will be intersecting both
triangles, but we should ignore the contact with the triangle that the
sphere is not directly above -> should ignore multiple contacts.

Now, ignoring multiple contacts is as easy as just using the contact with
the deepest penetration. But when should it be done? :)

ChrisC