patch for clang from Michel Morin

[SVN r78176]

include/boost/fusion/adapted/std_tuple/tag_of.hpp

@@ -10,12 +10,6 @@
 #include <tuple>
 #include <boost/fusion/support/tag_of_fwd.hpp>
 
-namespace std
-{
-    template <typename... Elements>
-    class tuple;
-}
-
 namespace boost { namespace fusion
 {
     struct std_tuple_tag;