Thanks to Vivian Meazza for debugging this. The output deque for
FGDigitalFilter was not being kept long enough for the
doubleExponential filter. Reads from output[1] could cause a crash.
SGPropertyNode to guarded ones. This is also done for JSBSim/JSBSim.hxx,
for which JSB had given explicit permission a while ago. I postponed that
back then, but now is the time.
I have implemented a Honeywell MK VIII EGPWS emulation for FlightGear.
The MK VIII is an Enhanced Ground Proximity Warning System aimed at
regional turboprop and small turbofan aircrafts such as the Citation,
Citation Bravo, B1900D, Beechcraft 99 and L410.
Frederic Bouvier:
make the MSVC compilation possible. Rearrange base package directories.
