Relay: Pixhawk AUXOUT2 enabled by default
Relay: param descr match labels for Pixhawk

Renamed Pixhawk FMU AUX1 to Pixhawk AUXOUT1 to match labels on case to
make it easier for users to know what value to choose
HAL_SITL: fixed handling of SIM_FLOAT_EXCEPT in main thread
AP_InertialSensor: fixed detection of dead IMU

if a PX4 sensor does not give new data we need to avoid calling
_rotate_and_offset_*() to avoid marking it as healthy. Otherwise if
the MPU6k dies we won't switch to the LSM303D automatically
HAL_Linux: fixed Replay with new AP_InertialSensor library
Replay: cope with up to 3 IMUs
AP_GPS: prevent bad NMEA strings from causing overruns in parser

fixes issue #961

thanks to crashpilot100 for spotting this!
AP_GPS: make NMEA driver a bit easier to read

thanks to crashpilot100
Plane: fixed handling of trim for flapersons

this allows TRIM_AUTO to work for flaperons

fixes issue #1188
Plane: started work on 3.1.2 release notes
Plane: mark beta2