Fix execution context of thread routines - note that this is not quite the architecture the Qt folks intended, but as they admit its the consequence of their architecture.

Conflicts:
	src/comm/QGCFlightGearLink.cc

Fixing -Wuninitialized

flightgear hil: correct scaling of pressure for mavlink message and remove indicated airspeed from flightgear protocol, commit requires flightgear protocol update

fix hardcoded start of fgfs and terrasync, use system environment variables for linux distro independence

re-enabled terrasync for all operating systems, might produce (non severe) errors on Windows or OS X