bugfix in code example

[[Imported from SVN: r5624]]

common/mpihelper.hh

@@ -43,7 +43,7 @@ namespace Dune
    *   \code
    *   int main(int argc, char** argv){
    *      typedef Dune::MPIHelper MPIHelper;
-   *      MPIHelper::instance(&argc, &argv);
+   *      MPIHelper::instance(argc, argv);
    *      typename MPIHelper::MPICommunicator world =
    *        MPIHelper::getCommunicator();
    *      ...