Plane: fixed previous_mode error in geofence 

when we were in MANUAL we would switch back to STABILIZE
AP_NavEKF : Add initial parameter defaults for Copter, Rover and Plane
Copter: spline bug fixes

Next waypoint's location must be passed in even if it's a straight
segment.
mission.get_next_nav_cmd's start_index should be the current command +1
WPNav: clean up spline comments
AC_AttControl: constrain earth frame yaw angle error

This temporarily resolves the wobble we see in Auto when the target
heading is suddenly changed leading to a large yaw angle error
Merge https://github.com/diydrones/ardupilot
AP_NavEKF : Fixes bug in initial earth magnetic field states

The calculation for these states was not being bias corrected
Merge https://github.com/diydrones/ardupilot