pyconfig.h must be included before any system header (as per Python docs; essential for Python 2.3 under Tru64 Unix)

[SVN r17799]

test/pickle2.cpp

@@ -20,8 +20,6 @@
     For more information refer to boost/libs/python/doc/pickle.html.
  */
 
-#include <string>
-
 #include <boost/python/module.hpp>
 #include <boost/python/def.hpp>
 #include <boost/python/class.hpp>
@@ -29,6 +27,8 @@
 #include <boost/python/extract.hpp>
 #include <boost/python/detail/api_placeholder.hpp>
 
+#include <string>
+
 namespace { // Avoid cluttering the global namespace.
 
   // A friendly class.