__sFILE is not exposed on OpenBSD

Index: python/python-libpst.cpp
--- python/python-libpst.cpp.orig
+++ python/python-libpst.cpp
@@ -7,6 +7,10 @@
 // #include <boost/python/docstring_options.hpp>
 // #include <iostream>
 
+#ifdef __OpenBSD__
+struct __sFILE { long dummy; };
+#endif
+
 extern "C" {
     #include "libpst.h"
     #include "timeconv.h"
