Plane: added RALLY_LIMIT_KM

this will prevent an embarressing use of a rally point from the wrong
airfield
Plane: honor zero RALLY_LIMIT_KM
HAL_Linux: use CLOCK_MONOTONIC_RAW to ensure clock never goes backwards

this avoids ntp mucking with APM timing
AP_HAL_FLYMAPLE: Improved libmaple version detection
AP_HAL_FLYMAPLE: UARTDriver begin now honours txS == 0 which means no change
AP_HAL_FLYMAPLE: FlymaplePortingNotes.txt improvements to install/build
documentation.
AP_HAL_FLYMAPLE: UARTDriver now uses the new libmaple tx ring buffers

This requires the libmaple fork at
https://github.com/mikemccauley/libmaple.git
which includes low level support for buffered usart transmits
APM_Control: improved auto docs for AP_SteerController
Rover: release beta7
Copter: pre-arm RC checks ch3's min and max
AC: fix autodocs for SUPER_SIMPLE so the GCSes can show the right options
Copter: correct HLD_LAT_P and HLD_LON_P ranges
AP_InertialSensor: added L3G4200D driver

this is for a cheap ebay 10DOF sensor
AP_InertialSensor: added L3G4200D example
DataFlash: prevent valgrind errors from Empty driver
HAL_Linux: better realtime setup

lock all memory and pre-fault the stack in all threads
HAL_Linux: don't prevent write while timer is busy

the timer can block on I2C writes, which causes the main loop to run
AP_Common: added product ID for L3G4200D
AP_Compass: prevent NULL deref on enable mag while running
AP_Compass: fixed orientation on Linux