Increase maximum target pitch to 20; useful at low speed.
Don't use *-trim flight controls. These were being left with non-zero values,
which then prevented other autopilot controllers from working properly.
For ailerons and elevators, incrase Kp at lower speeds, where faster movement
is needed. For elevators, also increase range to full +/-1 at lower speeds.
slowed down aileron movement slighly.
Reduced throttle gain to make things work more smoothly.
Deactivate auto-pilot if any wheel is touching the ground. This allows one to
(crudely) land using just the autopilot (in heading control and vertical speed
mode) with the arrow keys. Also deactivate if we are in replay mode to stop
visual fluttering of control surfaces when replaying.
