Parachute: set servo or relay to off position on every update

This resolves the issue of the parachute servo's position not being
initialised to the off position due to an ordering problem of the
auxiliary servos being initialised after the parachute object.
Copter: log DCM reported roll-pitch and yaw error
AP_Motors: reduce slow-start increment for fast CPUs
AP_Compass: use apply_correction_function to eliminate duplication
AP_Compass: added some comments
Replay: fixed printf format
AP_Airspeed: fixed airspeed in Replay
Replay: update for new copter ATTITUDE message
AP_Math: refactor quaternion library
AP_NavEKF: Quaternion::to_euler now uses references instead of pointers
AP_Math: fix up rotation test suite
AP_Math: change quaternion class to use const references where optimal
AP_Math: expand frame transformation test case for quaternions
PX4: try starting the ll40ls on either I2C bus
AP_Buffer: remove scalar assignment so that non-scalars can be buffered
AP_Buffer: Add peek_mutable function allowing in-place modification of buffered objects
AP_Buffer: change pop_front to return a bool if successful
GCS_MAVLink: merged upstream changes
GCS_MAVLink: added MAV_CMD_DO_LAND_START

see discussion on drones-discuss
GCS_MAVLink: re-generated headers