[ODE] enhanced ODE collision API

[David McClurg]

> geom groups are now spaces

does that mean a geom cannot be placed into two different groups?  not a big deal, but i'm curious.

> david - i think you mentioned that geoms might want to be interted into multiple spaces. can you give me a use case for this? - in the current API each geom has just one parent.

i just needed a way to implement collision filtering and the category and collide bitfields do this very elegantly!  thanks

one other common concept in collision detection is a ghost or phantom geom used as a sensor.  you don't bounce off it -- you just detect a penetration.  ie: what you want is just detection of the collision and not the contact information.  it would be nice if there was a built-in type called 'sensor' or something that didn't do the extra work of computing the contact point/normal.

that's it!  thanks to erwin for his contribs and i'm really excited about these developments.