Capture temporary by value.

The previous version should not have been worked since we stored
a reference to a temporary in the lambda. Surpisingly even
valgrind did not complain.

dune/solvers/solvers/criterion.hh

@@ -200,7 +200,7 @@ namespace Dune {
     Criterion maxIterCriterion(const SolverType& solver, int maxIterations)
     {
         return Criterion(
-                [&](){
+                [&solver, maxIterations](){
                     int i = solver.iterationCount();
                     return std::make_tuple( i>=maxIterations, Dune::formatString("% 7d", i) );
                 },