Make the falling animation work a bit better on fly-falling.
Implement IsTruelyColliding for avatars so that they can't climb up walls.
BulletSim: Add dylib for BulletSim
Merge in recent BulletSim commits.
No rotating avatars while on vehicles. Scale jumps so that they feel better. Fix sending enough updates for vehicles (since they update way more often than a normal physical prim).