autotest: added AVC_plane location

point along takeoff path
autotest: cope with newer versions of JSBSim
autotest: fixed problem with initial JSBSim headings to east

this avoids an auto-trim problem in JSBSim
autotest: convert Rascal back to a tail dragger
Plane: fixed zero throttle in FBWA glide failsafe
autotest: added -R to sim_vehicle.sh for reverse throttle
Rover: prevent unsupported command messages

this prevents errors on DO_CHANGE_SPEED
autotest: added TomCarpark test location
Rover: prepare for new beta
AP_Navigation: added a turn_distance() method with turn_angle
AP_L1_Control: implement turn_distance() with turn angle

uses a linear approximation for now.
Plane: calculate next_turn_angle to prevent early WP completion

this should help for ball drop and camera trigger with straight line
runs
GCS_MAVLink: added MAV_CMD_DO_INVERTED_FLIGHT

used to invert from a mission
GCS_MAVLink: rebuild MAVLink headers
AP_Mission: added support for MAV_CMD_DO_INVERTED_FLIGHT
Plane: added MAV_CMD_DO_INVERTED_FLIGHT support

allows for mission control over inverted flight