avoid compiler warning

[[Imported from SVN: r7293]]

dune/solvers/norms/h1seminorm.hh

@@ -43,7 +43,7 @@ public:
         // always scalar but the vectors may not be
         double sum = 0;
         
-        for (int i=0; i<matrix_->N(); i++) {
+        for (size_t i=0; i<matrix_->N(); i++) {
             
             typename Dune::BCRSMatrix<Dune::FieldMatrix<double,1,1> >::row_type::const_iterator cIt    = (*matrix_)[i].begin();
             typename Dune::BCRSMatrix<Dune::FieldMatrix<double,1,1> >::row_type::const_iterator cEndIt = (*matrix_)[i].end();