Unordered: Move the implementation into a namespace.

Although it typically won't prevent ADL, because of boost::hash.

[SVN r72391]

include/boost/unordered/detail/node.hpp

@@ -1,6 +1,6 @@
 
 // Copyright (C) 2003-2004 Jeremy B. Maitin-Shepard.
-// Copyright (C) 2005-2009 Daniel James
+// Copyright (C) 2005-2011 Daniel James
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)