message: mission: warn if changing takeoff/land to waypoint
  We should not silently change takeoff or land mission items to
  waypoints. We should at least warn the user about it, even though PX4 is
  supposed to do the right thing.
diff: @@ -1120,6 +1120,11 @@ Mission::Result MissionImpl::build_mission_items(MAV_CMD command,
  if (command == MAV_CMD_NAV_WAYPOINT || command == MAV_CMD_NAV_TAKEOFF ||
  command == MAV_CMD_NAV_LAND) {
  if (new_mission_item->has_position_set()) {
  + if (command == MAV_CMD_NAV_TAKEOFF) {
  + LogWarn() << "Converted takeoff mission item to normal waypoint";
  + } else if (command == MAV_CMD_NAV_LAND) {
  + LogWarn() << "Converted land mission item to normal waypoint";
  + }
  all_mission_items.push_back(new_mission_item);
  new_mission_item = std::make_shared<MissionItem>();
  }
  