AP_NavEKF : Clear compass fail on transition between armed and disarmed

This allows a compass that has been declared failed, possibly because of
external disturbances (eg movement of hatches, proximity of tools, etc)
to be given a second chance when the vehicle is armed.
Plane: don't do failsafe passthru with no RC input

thanks to Klrill-ka for the suggestion

fixes issue #1302
Copter: make landing detector more strict

Made more strict by requiring 50 consecutive iterations where the climb
rate is below +- 40cm/s.  Previously it was 50 cumulative.

Removed check of failsafe.radio when clearing the land flag because it
could result in the vehicle taking off if the user picked it up.
GCS_MAVLink: slow down parameter send a lot with no flow control
Plane: prepare beta4
Plane: prepare for 3.1.0 release
Rover: prepare for 2.46 release
AutoTest: reduce copter throttle when flying square

This will keep the copter lower during this test and resolve the timeout
during landing
LogAnalyzer: convert tabs to spaces (only) per coding conventions
LogAnalyzer: Report missing parameters as test failures
LogAnalyzer: If skipping badlines, ignore parse errors
Copter: remote arming check reference to compass learning
Copter: pre-arm check of internal vs ext compass
Plane: start working towards 3.1.1
Plane: use ground steering logic for final stage of auto landing

this should improve runway tracking
Plane: do landing flare if past landing point

this helps prevent us keeping the throttle on after we've landed if
the baro has drifted enough that we think we are not yet at the flare altitude
Plane: keep an estimate of the rangefinder altitude

only accept data when we have had 10 samples in a row in range at 50Hz
Plane: added RNGFND_LANDING option

this allows the use of a rangefinder for landing flare and landing
approach
HAL_SITL: fixed sonar correction for attitude
Plane: allow continued use of rangefinder data for 5s after loss of contact 

this allows short outages to be ridden out