Don't use the Element<N>::get way of accessing tuple elements.

It is not standard conforming.

[[Imported from SVN: r6657]]

dune/common/test/tuplestest.cc

@@ -79,7 +79,7 @@ int iteratorTupleTest()
 
   assert(get<2>(tuple_) == v.end());
   assert(get<0>(tuple_) != v.end());
-  assert(get<1>(tuple_)!= Element<2>::get(tuple_));
+  assert(get<1>(tuple_) != get<2>(tuple_));
   return ret;
 }