FlightGear - Flight Simulator FGAddon

* Checklists/takeoff.xml,
Models/Instruments/APpanel.xml,
Models/Instruments/FDpanel.xml,
Systems/ap-servos.xml,
Tutorials/Citation-II-tutorial-takeOff.xml,
states/approach-overlay.xml:
/autopilot/locks/passive-mode TRUE means the autopilot is OFF. This was
broken by r3883.

* Systems/fd1.xml: repair conditions to enable and disable various stages
This fixes pitch-hold and vertical-speed-hold broken in r3883.

* Nasal/citation2.nas (JetEngine.update): restore fuel flow broken in r3922.
(update_systems): Disengage autopilot at least 500 ft above ground again;
fixes regression introduced by r3883.