message: Add support to print `cv::UMat`.
  Now a user can use `std::cout` to print an object of `cv::UMat` just like `cv::Mat`.
diff: @@ -183,6 +183,12 @@ std::ostream& operator << (std::ostream& out, const Mat& mtx)
  return out << Formatter::get()->format(mtx);
  }
  +static inline
  +std::ostream& operator << (std::ostream& out, const UMat& m)
  +{
  + return out << m.getMat(ACCESS_READ);
  +}
  +
  template<typename _Tp> static inline
  std::ostream& operator << (std::ostream& out, const std::vector<Point_<_Tp> >& vec)
  {
  