[ODE] Trimesh-Trimesh and Triangle Normals

[Peter Kyme]

After struggling to figure out why I was getting such poor results with 
the trimesh-trimesh collider (despite the fact it seems to work quite 
well in Softimage XSI), I've finally found what appears to be the 
problem (for me anyway).

By adding one line that reverses the normals obtained for triangles on 
the 2nd trimesh, almost all of the problems I was seeing went away. This 
makes sense, since before this I would get contact normals facing in the 
wrong direction whenever a triangle normal from the 2nd geometry was used.

Can somebody (Jeff Smith?) explain why I needed to do this? Is it a 
symptom of another problem in the way I'm using the trimesh-trimesh 
collider?

The above also fixed the problems with the test_moving_trimesh demo as 
well for me (once the dGeomTriMeshDataSet call had been added).