Make it clear that only the menu directly passed to wxWindow::PopupMenu() doesn't need to be allocated on the heap and that its submenus still do. Closes #11851. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63771 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775