AP_Compass: improved COMPASS_ORIENT and COMPASS_EXTERNAL for Pixhawk
AP_InertialSensor: expose get_primary_accel() for use in AHRS
AP_AHRS: use primary accel for accel_ef

Logs from Randy show that the copter INav code can't handle the
accelerometer sensor changing.
AP_NavEKF : Increase the tuning range for magnetometer measurement noise
AP_AHRS: added get_fly_forward() method

will be used to detect a copter
AP_NavEKF: only use the active accel from DCM if fly_forward is set
AP_InertialSensor: Correct out-of-bounds array access that was causing SITL to crash
SITL: simulate dual accel/gyro
AP_NavEKF : Fixes zero compass offsets on initialisation
AP_NavEKF: give a sensible error for no such file on replay
Replay: moved replay tool into Tools/Replay
Replay: added parameter handling

use parameters from log, and allow override
Replay: added accel and gyro mask options
Replay: fixed -g option
AP_NavEKF : Add accel aliasing protection
AP_NavEKF : Add div0 protection to the IMU1_weighting calc
AP_NavEKF : Fix bug that prevents Zacc bias state variance being updated
AP_NavEKF : Use average of dual IMU gyro data when available
AP_NavEKF: don't assume the number of gyros == number of accels
AP_NavEKF: cope with compass going offline while in flight