COLLISION FLAGS

floor: for things that avatars can stand on
barrier: for things that avatars should collide against that are not floors
camera-collide: for things that the camera should avoid
trigger: for things (usually not barriers or floors) that should trigger an
         event when avatars intersect with them
sphere: for things that should have a collision sphere around them
tube: for things that should have a collision tube (cylinder) around them

NOTES

The barrier & camera-collide flags are typically used together.

Currently, the camera automatically pulls itself in front of anything
marked with the camera-collide flag, so that the view of the avatar isn't
blocked.

The trigger flag implies that avatars will not collide with the object;
they can move freely through it.

The sphere & tube flags create a collision object that is as small as
possible while completely containing the original flagged geometry.
