BulletSim: add ResetBroadphasePool and ResetConstraintSolver diagnostic
functions. If values set from console, the functions are called. Looking
for why the collision pools fill up with unnecessary stuff.
BulletSim: fix problem where pre-step actions would not replaced
by new registrations thus causing multiple instances of an action.
BulletSim: add comments to force and impulse setting functions
so it is clear what Bullet is actually doing with the set values.
BulletSim: reorganize motor code a little to pull together common functions.
Add BSFMotor.
BulletSim: add initial implementation of llMoveToTarget and hover height.
Not all there yet.
BulletSim: convert avatar movement from a force to an impulse. Shouldn't
change functionality but removes an oddity in computing the force.
BulletSim: add some features to the PID motor to make it more flexible.
BulletSim: implement llMoveToTarget by adding PIDActive, etc.
Implementation of non-vehicle hover but haven't tested it a lot.
Update TODO list.
BulletSim: fix problem where mesh shapes were physically just their bounding box and not the complete mesh. Fill mesh physical objects are back.