[ODE] Compiling Problem dHeightfield

[David Walters]

> I would say that trimesh-heightfield collision would probably be good

Right, that's in now. NOTE: I've tested in Visual Studio 2003 only.

One thing I noticed is that in debug builds it became pretty slow when
a bunny was dropped. The same slowdown didn't seem to be noticable in
a release build. Anyway, functionally it's in - bug fixes then
optimisation are the next steps if anyone wants to volunteer :-)

Regards,
Dave.

ps. I've updated the grid in the wiki to reflect this addition.