[ODE] enhanced ODE collision API

[Erwin de Vries]

> 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.

I proposed this once. Calling dCollide() with 0 as flags, and simply have it
return 0 or 1. It would be entirely possible, but it could break old code.
But i doubt anyone does it this way.

Erwin