Hash: Merge deprecated header warning + some documentation.

[SVN r78697]

hash/test/deprecated_container_fwd.cpp

@@ -0,0 +1,14 @@
+
+// Copyright 2012 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)
+
+#include <boost/functional/detail/container_fwd.hpp>
+
+typedef std::vector<int, std::allocator<int> > int_vector;
+
+#include <vector>
+
+int main() {
+    int_vector x;
+}