Also add wxNonOwnedWindow for wxMSW (which previously simply typedef'd it to
wxWindow) and document this class now that it provides some user-visible
functionality.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69364 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775