Avoid overriding wxDirDialog::GetPath[s]() unnecessarily

Don't duplicate practically the same code in all ports, just add m_paths
itself to the base class. The only drawback of doing this is that it's
unused in the ports not (yet) using it, but this saves enough code in
the aggregate to be worth it.

src/msw/dirdlg.cpp

@@ -151,19 +151,6 @@ void wxDirDialog::SetPath(const wxString& path)
     }
 }
 
-wxString wxDirDialog::GetPath() const
-{
-    wxCHECK_MSG( !HasFlag(wxDD_MULTIPLE), wxEmptyString,
-         "When using wxDD_MULTIPLE, must call GetPaths() instead" );
-
-    return m_path;
-}
-
-void wxDirDialog::GetPaths(wxArrayString& paths) const
-{
-    paths = m_paths;
-}
-
 int wxDirDialog::ShowModal()
 {
     WX_HOOK_MODAL_DIALOG();
@@ -293,7 +280,7 @@ int wxDirDialog::ShowIFileOpenDialog(WXHWND owner)
     {
         if ( !HasFlag(wxDD_MULTIPLE) )
         {
-            m_path = m_paths.front();
+            m_path = m_paths.Last();
         }
 
         return wxID_OK;