Copter: slow motors after landing in AUTO

This resolves an issue in which the vehicle could tip over if the pilot
did not reduce the throttle to zero soon after landing in AUTO mode

ArduCopter/control_auto.pde

@@ -269,7 +269,7 @@ static void auto_land_start(const Vector3f& destination)
 static void auto_land_run()
 {
     // if not auto armed set throttle to zero and exit immediately
-    if(!ap.auto_armed) {
+    if(!ap.auto_armed || ap.land_complete) {
         attitude_control.relax_bf_rate_controller();
         attitude_control.set_yaw_target_to_current_heading();
         attitude_control.set_throttle_out(0, false);