[ODE] 2d system

[Christopher Jefferson]

Hi!
I would like to use ODE in a 2 dimensional system. I notice from the
documentation that 2d is mentioned in the changelog but can't find it
anywhere else. To simple get me started I decided to try using spheres and
cubes and set the co-ordinates appropriately. This does work at first but
unsurprisingly it slowly drifts into the third dimension. I can keep
forcing things back into 2d but I was wondering if there is a better way to
do this?
Chris