Revert Stephen Kelly's changes.

They should really wait until MPL's dependencies have dealt with his
changes.

include/boost/mpl/set/aux_/iterator.hpp

@@ -44,8 +44,12 @@ template< typename Set, typename Tail > struct s_iter_impl
     typedef forward_iterator_tag        category;
     typedef typename Tail::item_type_   type;
 
+#if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
+    typedef typename s_iter_get< Set,typename Tail::base >::type next;
+#endif
 };
 
+#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
 
 template< typename Set, typename Tail > 
 struct next< s_iter<Set,Tail> >
@@ -69,6 +73,25 @@ template< typename Set > struct s_iter<Set, set0<> >
     typedef forward_iterator_tag category;
 };
 
+#else
+
+template< typename Set >
+struct s_end_iter
+{
+    typedef forward_iterator_tag    category;
+    typedef s_iter<Set,set0<> >     next;
+};
+
+template< typename Set, typename Tail > struct s_iter
+    : if_< 
+          is_same< Tail,set0<> >
+        , s_end_iter<Set>
+        , s_iter_impl<Set,Tail>
+        >::type
+{
+};
+
+#endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 
 }}