[committed] 1-line change to support collision use case

I don't see why you would ever want to check spatial collision with itself, so I fully support this change.

Other than some sort of "self-intersection" during an animation, I can only really think of if you want to see if an object collides with some part of it, e.g. a hand colliding with your head. Technically it all belongs to the same object. Practically I'm sure, that wouldn't be needed (e.g. we'd have animations) and if it is needed, it can just be modeled as two separate objects.

So I would say this is a practical change.

I think it would still be the case, that if you checked for collisions of the hand itself, you would get a result - just not if you checked for collisions on the person. I think if you want resutls on a specific part it's reasonable to check at that level.

My work around for this is not nearly so neat - seems like a good move.

Committed with rev 4400