message: Minor fix in concat_view()
diff: @@ -699,13 +699,10 @@ template<typename RHS_T, typename ... Ts>
  DataFramePtrView<I>
  DataFrame<I, H>::concat_view(const RHS_T &rhs, concat_policy cp) const {
  - static_assert((std::is_base_of<StdDataFrame<I>, RHS_T>::value ||
  - std::is_base_of<DataFrameView<I>, RHS_T>::value ||
  - std::is_base_of<DataFramePtrView<I>, RHS_T>::value) &&
  + static_assert(! std::is_base_of<StdDataFrame<I>, RHS_T>::value ||
  ! std::is_base_of<StdDataFrame<I>, decltype(*this)>::value,
  - "The rhs argument to concat_view() can only be "
  - "StdDataFrame<IndexType> or DataFrame[Ptr]View<IndexType>. "
  - "Self must be StdDataFrame<IndexType>");
  + "Currently, arguments to concat_view() can only be "
  + "StdDataFrame<IndexType>.");
  DataFramePtrView<I> result;
  