AP_GPS: prevent writing GPS log headings multiple times
AP_NavEKF: fixed some matlab ! -> ~ typos

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
Replay: cope with too many log format msgs
APM_Control: logging_started needs to be static

prevents writing log headers twice
AP_HAL: added set_failsafe_pwm() API

this allows the PWM values for FMU firmware failure to be setup
RC_Channel: added setup_failsafe_trim_all() function

sets all channels to output trim values on FMU failure
Rover: setup failsafe trim values for if FMU firmware dies
Plane: setup failsafe trim values for if FMU firmware dies
Copter: STB_RLL_P and STB_PIT_P @Range 3 to 12
RC_Channel: added support for LimitValue settings

this allows you to set a channel failsafe or radio_out to a limit
value
APM_OBC: setup termination values in PX4IO

this sets up the PX4IO board with failsafe values in case the FMU is
not running
Plane: use new APM_OBC API
Plane: setup failsafe values for OBC in failsafe callback
Replay: added -A option to set arming time
AP_NavEKF: fixed millisecond subtraction for rollover

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
PosControl: update_pos_controller renamed to update_xy_controller
Circle: integrate update_xy_controller name change
AC_WPNav: integrate update_xy_controller name change
Copter: set main loop rate from CPU class

Previously this was determined by the board
AC_WPNav: run loiter and wp nav at 50hz on Pixhawk