Header dependency cleanup. Removed some standard includes, splitted large "utilities" headers, and minimized algorithm dependencies.

include/boost/intrusive/unordered_set.hpp

@@ -1,7 +1,7 @@
 /////////////////////////////////////////////////////////////////////////////
 //
 // (C) Copyright Olaf Krzikalla 2004-2006.
-// (C) Copyright Ion Gaztanaga  2006-2013
+// (C) Copyright Ion Gaztanaga  2006-2014
 //
 // Distributed under the Boost Software License, Version 1.0.
 //    (See accompanying file LICENSE_1_0.txt or copy at
@@ -17,6 +17,8 @@
 #include <boost/intrusive/intrusive_fwd.hpp>
 #include <boost/intrusive/hashtable.hpp>
 #include <boost/move/utility_core.hpp>
+#include <boost/static_assert.hpp>
+
 #include <iterator>