add unit test around Mat::push_back()

add template specialization Mat::push_back() for MatExpr paramters

extend push_back MatExpr to mat in unit test

cast to object instead of reference

test with multi-row MatExpr input

modules/core/include/opencv2/core/mat.inl.hpp

@@ -1096,6 +1096,12 @@ void Mat::push_back(const Mat_<_Tp>& m)
     push_back((const Mat&)m);
 }
 
+template<> inline
+void Mat::push_back(const MatExpr& expr)
+{
+    push_back(static_cast<Mat>(expr));
+}
+
 ///////////////////////////// MatSize ////////////////////////////
 
 inline