[ODE] better way to handle terrain

[Chris Ledwith]

> believe it or not, my past experience with ODE collision library proves
> that
> a single merged tri-mesh collision geom is faster than 'chunked'
> tri-meshes... and yes, the 'chunked' way was my first trial coz it
> should --in theory-- be faster, but after some testing and coding
> iteration
> to enhance our fps stats, it shown that merging all tri-mesh geoms result
> in
> fastest 'updates' in our implementation case... but again, as the ODE doc
> says, your mileage may vary :).
> I think it depends on how you define 'huge' is...
>
> Tri S.
>

It works well because OPCODE automatically generates an AABB tree for each
trimesh, which improves speed, just as if you split the terrain up
yourself.

-Chris