use std::cout to avoid a format warning

[[Imported from SVN: r7395]]

dune/solvers/iterationsteps/mmgstep.cc

@@ -218,8 +218,8 @@ void MonotoneMGStep<MatrixType, VectorType>::iterate()
                     
                     std::cout << "Obstacle disregarded!\n";
                     std::cout << (*x[level])[i] << std::endl << obstacles[level][i] << std::endl;
-                    printf("level: %d   index: %d   komponent: %d\n", level, i, j);
-                    printf("is %s critical\n", (critical[i][j]) ? "" : "not");
+                    std::cout << "level: " << level << "   index: " << i << "   komponent: " << j << std::endl;
+                    std::cout << "is " << ((critical[i][j]) ? "" : "not") << "critical" << std::endl;
                 }
 #endif