Move the hash extensions into their own header, which hopefully makes the

extension implementation a little clearer. It also fixes a problem where the
visual C++ include once pragma was preventing the extensions from being loaded
on the second include.


[SVN r35314]

include/boost/functional/hash.hpp

@@ -8,3 +8,7 @@
 //  issue 6.18. 
 
 #include <boost/functional/hash/hash.hpp>
+
+#if !defined(BOOST_HASH_NO_EXTENSIONS)
+#include <boost/functional/hash/extensions.hpp>
+#endif