Copter: update firmware version to AC3.1-rc3
GPSGlitch: parameters for accel and always-ok-radius
AutoTest: slightly shorten copter loiter test
AutoTune: abandon tuning if rate P hits minimum

Fixes from Leonard
Copter: pre-arm expects mag len of 330 for APM1 (was 530)
HAL_Linux: use larger UART buffers

might as well use the memory
HAL_Linux: run threads a bit more slowly

this was just wasting cycles
AP_BattMonitor: fixed type in docs
Copter:Parameter descriptions updated
AP_BattMonitor: Updated parameter descriptions
Iris: Updated Parameter file for rc3
AP_InertialSensor: remove unused get_last_sample_time_micros()
AP_HAL: fixed example build
AP_InertialSensor: don't build L3G4200D example
autotest: tweak plane autotest debugging
GCS_Console: don't build this example

it doesn't build any more
BattMon: amp-per-volt reduced to 17 (was 18.002)
Iris: fix typo in param file
Iris: enable throttle failsafe

Set to always RTL
Iris: enable Altitude fence by default