- changed all sound file properties to end in /path for pathname, and
added /sound and /pitch (with current values as defaults)
- don't activate the stall horn if CAS is less than 30kt (this needs
to be refined somehow)
- declarations to support changes to cxx file
- delete table in destructor
** src/FDM/flight.cxx
- bind engine properties in FGInterface::bind, and publish properties
for all engines rather than just engine 0
** src/Main/fg_props.cxx
- removed all engine properties; now bound in FGInterface::bind
** src/Sounds/fg_fx.cxx
- support multiple engine and cranking sounds
** src/Sounds/fg_fx.hxx
- support multiple engine and cranking sounds
