[ODE] Demo of buoyancy and ODE

[Mattias Fagerlund]

> Very cool.  Be interesting to try this on a complex shape - have you
> tried something like a boat mesh?

Well, since I aproximate bodies through spheres, a boat mesh isn't 
possible to simulate in itself, only the aproximation. It's a bit like 
using spheres and boxes to aproximate colission/dynamics objects. But no, 
I haven't created a complex aproximation yet, it'd be interesting to see 
how it came out. It's in the pipeline though.

cheers,
m