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
AP_Mission: Added support for MAV_CMD_DO_LAND_START
Plane: Added support for MAV_CMD_DO_LAND_START
Plane: Added parameter RTL_AUTOLAND and implementation.
AP_AHRS: make get_position() const

This allows use from within AP_Mission
AP_Mission: avoid the AP_AHRS cast

get_position() is now const
Plane: improved check for reaching RTL point for auto-land
Plane: switch to AUTO on a DO_LAND_START MAVLink command