AP_TECS : Prevent throttle undershoot after climb

If the plane was unable to achieve the climb and got significantly below the internal TECS demanded climb profile, the the PD term would be a large value at the top of climb, and would take some time to reduce due to the rate limiter. This meant that the integrator state could be pushed to a very low value and effectively cause the throttle to sit on the lower limit for longer than desired after levelling out.
AP_TECS: fixed throttle demand on underspeed

thanks to Philipp Oettershagen for finding this bug!
AutoTest: fix fly_mission to recognise end of mission

Copter's behaviour after completing a mission has changed so it does not
automatically switch to Loiter mode but rather stays at the last
waypoint.  This was confusing the fly_mission function.
HAL_PX4: use px4io generated values for servo output readback

this makes it easier to observe the behaviour of IO failsafe
Copter: remove abbreviations from GCS messages
Copter: allow starting autotune from flightmode switch

ch5 switch to AutoTune is equivalent to starting autotune via sw7/8.
Copter: minor reformat of control_autotune