Revert Stephen Kelly's changes.

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

include/boost/mpl/empty_base.hpp

@@ -34,12 +34,18 @@ template< typename T >
 struct is_empty_base
     : false_
 {
+#if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
+    using false_::value;
+#endif
 };
 
 template<>
 struct is_empty_base<empty_base>
     : true_
 {
+#if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
+    using true_::value;
+#endif
 };
 
 }}