Plane: change to 2.74beta3
Plane: fixed FBWB airspeed control

thanks to Gabor for reporting this!
documentation: minor fix to px4 build instructions (tridge please check)
WPNav: stopping point projection uses wp_leash
Copter: project stopping point for loiter command
Copter: increase Yaw Rate I 0.02
Copter: revert Loiter Pos P to 1.0 (was 0.8)
HAL_PX4: added GPIO driver
AP_Relay: setup pin for PX4 relay support
PX4: enable mkblctrl driver
PX4: added support for mkblctrl driver

this enables runtime support for the mkblctrl I2C ESC drivers
HAL_PX4: retry opening UARTs up to 5 times

this seems to help a lot with the USB port on PX4
HAL_PX4: fixed definition of relay and piezo pins
AP_Relay: update for new PX4 relay pin
Copter: fixed build with specified GPS driver
OptFlow: initialisation fix

Thanks to DongFang (aka Soren) for finding the issue and the solution
Copter: firmware version to 3.0.1
Copter: Body frame ACRO upgrade
TradHeli: compile error fix related to new ACRO

The motors_runup_complete must be a feature that Rob has implemented in
his clone which has not yet reached master.  We will need to restore
these lost few trad-heli specific lines once Rob's changes make it to
master.