[ODE] new ODE collision

[David McClurg]

should it be allowable to have an empty space in another space?  it is convenient for my application because i add/remove geoms to/from groups on the fly to optimize collisions.

if it's ok and i'm pretty sure it used to work with an empty group inside a hash space, then i think there is a problem.  currently, i get a floating point invalid operation in findLevel() because q=dInfinity

  frexp (q,&level);

this is because the AABB for an empty group (ie, simple space) is set to infinities in dxSpace::computeAABB() in collision_space.cpp