MAVLink: update to latest upstream message defintions XML

this adds new HIL support for airspeed, and common SIM_STATE and
RADIO_STATUS messages
Plane: update takeoff course when conditions met

This allows for change of heading before the final takeoff conditions
are met

thanks to Greg Fletcher for suggesting this
Plane: update FS_LONG_ACTN and FS_SHORT_ACTN docs

thanks to Craig for noticing this