FlightGear - Flight Simulator FGAddon

* Pushback is only visible if
airplain on ground
slower then 10 feets per second
* parking brake are engaged if pushback is not linked but enabled
* parking brake are released if pushback is linked
* thrust pulled to idle if the engines are running and pushback is enabled
it is possible to spool up and down the engines and
also to deploy and stow the reverser
This means the pilot have no handycap with the procetures while pushback
* fixed thrust bug while engines stopped