native GTK 2.4 file dialogs into one place by making wxFileDialog derive from the generic variant and by then choosing which implementation to use. Later, we'll add run-time checks. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30868 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775