AntennaTracker: added sending on SIMSTATE in SITL
autotest: raise turn rate of antennas
autotest: kill off old tasks on exit
Rover: fixed comment
Plane: print PX4 compass type
AP_Compass: fixed showing of is_external for 2nd compass
AP_NavEKF : Update comments and remove un-used function declarations
AP_NavEKF : Use synthetic sideslip fusion during GPS denied operation with airspeed
Copter : start dataflash logging on initialisation to aid EKF debugging
Merge branch 'ekf-wip' of https://github.com/priseborough/ardupilot into ekf-wip

# By Paul Riseborough
* 'ekf-wip' of https://github.com/priseborough/ardupilot:
  Copter : start dataflash logging on initialisation to aid EKF debugging
  AP_NavEKF : Use synthetic sideslip fusion during GPS denied operation with airspeed
  AP_NavEKF : Update comments and remove un-used function declarations