Don't use global index set of dune-functions basis

dune/fufem/functionspacebases/dunefunctionsbasis.hh

@@ -56,7 +56,7 @@ public:
    */
   size_t size() const
   {
-    return dfBasis_.indexSet().size();
+    return dfBasis_.size();
   }
 
   /** \brief Get a local finite element (i.e., a set of shape functions) for the given element