message: prevent copying in cv::Mat_<T> move assignment
diff: @@ -1818,7 +1818,7 @@ Mat_<_Tp>::Mat_(Mat_&& m)
  template<typename _Tp> inline
  Mat_<_Tp>& Mat_<_Tp>::operator = (Mat_&& m)
  {
  - Mat::operator = (m);
  + Mat::operator = (std::move(m));
  return *this;
  }
  