Don't compile this if not using MDI

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@24790 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/mdi.h

@@ -1,6 +1,10 @@
 #ifndef _WX_MDI_H_BASE_
 #define _WX_MDI_H_BASE_
 
+#include "wx/setup.h"
+
+#if wxUSE_MDI_ARCHITECTURE
+
 #if defined(__WXUNIVERSAL__)
 #include "wx/generic/mdig.h"
 #elif defined(__WXMSW__)
@@ -17,5 +21,7 @@
 #include "wx/stubs/mdi.h"
 #endif
 
+#endif // wxUSE_MDI_ARCHITECTURE
+
 #endif
     // _WX_MDI_H_BASE_