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
AP_Scheduler: improved the accuracy of the scheduling code

prevent accumulated micros() errors in run()
autotest: speed up build_all_px4.sh

only build archives once
AP_Scheduler: show slips only for SCHED_DEBUG>1

this allows us to see PERF reports in copter without console writes
slowing things down
HAL_AVR: reduce the latency of semaphore waits

this reduces the average cost of waiting for the MPU6000 semaphore
from the main loop
Rover: prepare for 2.43 release