2. also implement Getcolumn/RowCount() in it now and document them
3. removed various remains of old (pre-wxRadioBoxBase) cruft
sorry in advance for any compilation breakage on the platforms I can't test on
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@36307 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775