avoid signed/unsigned warning

[[Imported from SVN: r6331]]

dune/solvers/norms/h1seminorm.hh

@@ -21,7 +21,7 @@ public:
 	{
 		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();