include iostream header when using std streams

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@43015 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/docvwmdi/doc.cpp

@@ -19,12 +19,17 @@
 #ifndef WX_PRECOMP
 #include "wx/wx.h"
 #endif
-#include "wx/txtstrm.h"
 
 #if !wxUSE_DOC_VIEW_ARCHITECTURE
 #error You must set wxUSE_DOC_VIEW_ARCHITECTURE to 1 in setup.h!
 #endif
 
+#if wxUSE_STD_IOSTREAM
+    #include "wx/ioswrap.h"
+#else
+    #include "wx/txtstrm.h"
+#endif
+
 #include "doc.h"
 #include "view.h"