HAL_PX4: enable ttyACM0 as main console, ttyS1 as telemetry port
HAL_PX4: perform automatic update of px4io firmware
Plane: enable PX4IO dual telemetry devices
HAL_PX4: cope with O_NONBLOCK not working in NuttX on ttyACM0

writes will block anyway, which clags up APM
AP_InertialSensor: return roll and pitch trim angles
Copter: integrate automatic roll and pitch trims
Plane: integrate automatic roll and pitch trims
Rover: integrate automatic roll and pitch trims
Copter: update firmware version to 2.9.1-rc1
Copter: updated release notes for 2.9.1-rc2
Copter: update version to 2.9.1 ahead of release
AHRS: limit trim to 10 degrees
AHRS: fix example sketch to use roll/pitch trim
Plane: fixed a bug with setting stream rates 

this is what caused the "no sensors" problem in the 2.69 release
Plane: default the stream rates to 1Hz
HAL_PX4: changed scheduler priorities

put sensor priority above main sketch, to prevent occasional blocking
for sensor data
AP_GPS: removed unused AP_GPS_Shim.h
AP_GPS: ensure constructors zero all key variables

this prevents a crash on PX4 if a GPS is attached after startup
Plane: reset AHRS trim after a level operation
Rover: reset AHRS trim after levelling