Fix some compilation and linking errors in samples.

Replace some calls to wxString::getWriteBuffer with
wxStringBuffer.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@22107 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/variant.h

@@ -19,6 +19,7 @@
 #include "wx/defs.h"
 #include "wx/object.h"
 #include "wx/string.h"
+#include "wx/arrstr.h"
 #include "wx/list.h"
 
 #if wxUSE_DATETIME