Plane: mark ArduPlane 2.74beta
Copter: log compass failur to dataflash
Merge branch 'master' of https://github.com/diydrones/ardupilot
Copter: restore logging of arm/disarm event
Copter: remove unused event definitions
Copter: update firmware version and release notes ahead of -rc2
Copter: flexible CH6 declination tuning range
Copter: change to default RTL yaw behaviour

We will not point the nose home for RTL but will point the nose for all
other waypoints
Copter: bug fix for POSITION mode throttle

Was using alt-hold throttle controller instead of manual throttle
controller
DataFlash: prevent the dataflash erase problem

only allow writes to dataflash block devices once StartNewLog() has
been called
AP_Motors: motor_enabled array to bool

Also increased the default MAX_THROTTLE from 850 to 1000 but this number
is always overwritten by the main code anyway so should have no
functional impact.
Copter: remove unused TB_RATIO parameter
ACMotors: ESC Calibration only for enabled motors
ACMotors: remove unused get_num_motors function

Saves about 4 bytes of RAM
ACMotors: make a few functions non-virtual
ACMotors: make test_order uint_8
ACMotors: make a few more functions non-virtual

Saves at least 22 bytes of RAM
ACMotors: small formatting change
WPNav: divide by zero checks
Copter: change to compassmot instructions