AC_AttControl: bug fix for ef target during acro
Copter: add pitch axis flipping

Added Pitch axis flipping. You must be pushing forward or back 3° to make it flip in Pitch axis or it will flip in the default roll axis.
Added some extra throttle control to maintain altitude
removed the CH7 ability to exit Flip mode. It will exit only if completing flip or user aborts with control sticks.
Copter: flip minor comments and formatting
Copter: remove unused flip_stop
Copter: ensure motors don't stop during flip
Plane: added FBWA_TDRAG_CHAN parameter

this allows for testing taildragger takeoffs in FBWA mode
AP_NavEKF: make use_compass() public
AP_AHRS: use EKF use_compass() if EKF enabled

this allows magfailed status to show on console via SYS_STATUS health
bits
Plane: reset steering integrator on mode change and when not moving

this prevents an old integrator from causing problems on takeoff
AP_Terrain: fetch more terrain data around waypoints

this ensures we have data for a wide region (1km) around each waypoint
Plane: run terrain.update() more often

this provides faster checking of mission waypoints
AP_Mount.cpp - correct units in description

That should be corrected also in MP as the current code is expecting
degrees, not centidegrees.
3dr Berkeley moved - updated coords
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