AP_NavEKF : modifed Zaccel bias noise parameter to prevent unstable bias estimate
Copter: removed check on target component in arm

Thanks to DonLakeFlyer for finding this, see
https://github.com/diydrones/ardupilot/pull/909
Plane: removed check on target_component in ARM/DISARM

Thanks to DonLakeFlyer for finding this, see
https://github.com/diydrones/ardupilot/pull/909
AP_Relay: fixed Pixhawk relay pin numbers

thanks to Craig for spotting this!
DataFlash: Add Log_Write_Radio to store RSSI and noise on board.
GCS_MAVLink: allow logging of RADIO_STATUS, very useful for link analysis
Plane: Add Log_Write_Radio. MASK_LOG_PM must be set for logging to occur.
Copter: enable logging of RADIO_STATUS
Rover: enable logging of RADIO_STATUS
GCS_MAVLink: merge XML from upstream
GCS_MAVLink: re-generate MAVLink headers
Frame_params: Added Iris with Tarot Gimbal
Frame_params: Updated Iris.param
AP_Common: make alt in Location 24 bit

this allows for up to 83km mission altitudes, while allowing for 1
more byte in the command structure, making p1 16 bits
AP_Mission: make p1 16 bit

this gives us a 16 bit value for extra data on a location, allowing
for an accurate angle in centi-degrees.

Also add validation of the size of the union arms in Content
AP_TECS: New params LAND_ARSPD and LAND_THR auto-slowing landings.

Also controlling pitch by ignoring height error during landing.
This serves to keep the nose up.
AP_TECS: Auto landing now takes throttle_nudge into account.
AP_SpdHgtControl: added get_target_airspeed() interface
Plane: use TECS get_target_airspeed()
AP_TECS: make target landing speed a float

some users may want more precise control