FlightGear - Flight Simulator FGAddon

* Do not pollute the property trees of remote aircraft over multiplayer:
find Models/ -name '*.xml' -exec sed -r -i 's,>/,>,g' {} \;
* Models/Interior/Panel/Instruments/rpm/rpm.xml: one revolution of the needle per 1000 rpm
instead of per 10k RPM. Makes the instrument much more usable.
* Systems/f6f-keyboard.xml, Systems/help.xml: Alt+S to toggle supercharger speed.
* f6f-base.xml: initialize property for supercharger speed. Allow-toggle-cockpit: true.
* f6f-yasim.xml: rewrite performance numbers to allow landing. Previously, the propeller
thrust at idle was such that even with full flaps, airspeed would not drop below 90 knots,
preventing landing.
Also, implement the two-speed, two stage supercharger of the R-2800. Low speed can
maintain 56" of manifold pressure (!) up to 14500 ft; high speed up to 23500 ft. Not
implemented is the power drawn by the supercharger.