Allows for using a non-templated destructor in a unique_ptr, able to destroy
an upcasted pointer too. At the moment, we just introduce an extra dependency
on Boost.Intrustive; we should report this bug upstream with a MWE.

--- boost/move/detail/unique_ptr_meta_utils.hpp.orig	2014-11-05 13:36:28.212289350 +0100
+++ boost/move/detail/unique_ptr_meta_utils.hpp	2014-11-05 14:31:35.360395529 +0100
@@ -14,6 +14,8 @@
 #ifndef BOOST_MOVE_UNIQUE_PTR_DETAIL_META_UTILS_HPP
 #define BOOST_MOVE_UNIQUE_PTR_DETAIL_META_UTILS_HPP
 
+#include <boost/intrusive/pointer_traits.hpp>
+
 #include <cstddef>   //for std::size_t
 
 //Small meta-typetraits to support move
@@ -383,7 +385,7 @@
 template <class T, class D, bool = has_pointer_type<D>::value>
 struct pointer_type_imp
 {
-    typedef typename D::pointer type;
+    typedef typename boost::intrusive::pointer_traits<typename D::pointer>::template rebind_pointer<T>::type type;
 };
 
 template <class T, class D>