https://github.com/ArduPilot/ardupilot/pull/5135

thanks to Buzz for noticing!

this removes the zero of roll, pitch and yaw integrator on mode
change, now only doing the steering integrator.

The zeroing was from the early days when our controllers were not as
good. It should not be needed any more.

- update_flight_stage is already called within restart_landing_sequence()

- move functions restart_landing_sequence() and jump_to_landing_sequence() to AP_Landing
- NOTE: jump_to function can not set mode, so it is now done externally in vehicle

to ensure px4io is setup first

Using a global .dir-locals.el file is a better alternative than
reincluding the same emacs header in every file of the project.

thanks to Tim Gold for reporting this

we need to prevent RC overrides within px4io from running

this allows BoardConfig to report errors in a way that allows for
BRD_TYPE to be changed by the user

this fixes a problem where modes like loiter and auto would allow for
rudder stick mixing even with STICK_MIXING=0