[ODE] Terrain collision.

[Geoff Carlton]

I adapted ode to have a massive, dynamically loading world.  I broke it 
into squares of about 2000x2000m each.  Each square had its own trimesh 
geom, as well as all the entities in that region.

Also, each region had its own units, with the origin at the square's 
centre.  This technique could be used for pretty much any sized world.  
Collisions across boundaries were done by translating the target object 
into the new square's space (e.g. teleporting it 2000 units away, 
testing, then teleporting 2000 units back) - that aspect needed a bit 
more work to get correct results, so there were glitches going across 
square boundaries. 

The hard part is really not ode, its the rest of the game.  Once you've 
got the proper partioning framework (plus network code etc), plugging 
ode in shouldn't be too bad.

Geoff