FlightGear - Flight Simulator FGAddon

* Models/mosquito.ac: move the back of the navigator seat aft so that
the fuel cocks become visible and accessible.
* mosquito-common.xml (sim/help/text): Add engine startup and other
instructions.
* mosquito-yasim.xml: the engines are supercharged, not turbocharged.
* Nasal/failure.nas: make the copilot tell what happens to the aeroplane.