[ODE] correctly using dContactGeom structur

[Geoff Carlton]

Christoph Beyer wrote:
> Well, i will ignore 'side1' and 'side2'.
>
>   
The side fields give additional information about what part of the geom 
collided.   For trimeshes, it is obviously the trimesh index.   For 
boxes, I don't believe it is used.  In theory it could hold something 
like 0..5 as the closest side, or 6..13 for corner collisions.

For something like a cylinder, if you easily had the information, you 
could return 0 for the wrapping part, 1 for the top plate or 2 for the 
bottom plate. 

That sort of thing helps if the application wants special behaviour on 
certain surfaces (sparks, friction, etc).  It isn't that essential and 
I'm sure there is no problem leaving it blank, however.

Geoff