Add tests for linking two object files that include the hash libraries.

[SVN r29710]

test/link_test_2.cpp

@@ -0,0 +1,9 @@
+
+//  (C) Copyright Daniel James 2005.
+//  Use, modification and distribution are subject to 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)
+
+#include <boost/functional/hash.hpp>
+
+int f() { return 0; }