Mission: fix CHANGE_ALT to store climb rate in lat param

The slightly confusing storage of climb rate in the lat field led to a
bug fix a few months ago that actually created a bug.
Copter: check target of set-mode request from GCS

Issue discovered and fix contributed by Deadolous
Copter: remove unused AIRFRAME definition
Copter: print frame type in log headers
Compass: param descriptions for OFS2, MOT2
INS: param descriptions for ACC2, GYR2
LogAnalyzer: add POSHOLD to TestPitchRollCoupling
AC_WPNav: add shift_wp_origin_to_current_pos for takeoff

This shifts the origin to the vehicle's current position and should be
called just before take-off to ensure there are no sudden roll or pitch
moves on takeoff.
Copter: shift pos targets to current location before takeoff