Added method vector to const iterator.

[[Imported from SVN: r1681]]

fem/common/dofiterator.hh

@@ -187,6 +187,8 @@ namespace Dune {
       it_.reset();
     }
 
+    const DofType * vector () const { return it_.vector(); }
+
   private:
     DofIteratorImp it_;
   }; // end class DofIteratorDefault