Add mp_quote, mp_unquote.

test/mp_quote.cpp

@@ -0,0 +1,28 @@
+
+//  Copyright 2015 Peter Dimov.
+//
+// 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/mp11/utility.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+struct X {};
+
+int main()
+{
+    using boost::mp_identity_t;
+    using boost::mp_quote;
+    using boost::mp_unquote;
+
+    using Q = mp_quote<mp_identity_t>;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_unquote<Q, void>, void>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_unquote<Q, int[]>, int[]>));
+
+    return boost::report_errors();
+}