In verbose mode, print a message if the initial iterate is accepted

Previously, if the subdifferential at the initial iterate would contain zero,
no message would be written at all.  This made it more difficult to follow
the programm output, because it was impossible to see how many times
the bisection method was called.

dune/tnnmg/problem-classes/bisection.hh

@@ -74,7 +74,11 @@ class Bisection
             J.subDiff(x, DJ);
             ++count;
             if (DJ.containsZero(safety_))
+            {
+                if (verbosity > 0)
+                    std::cout << "Bisection: initial iterate " << x << " accepted, DJ = " << DJ << std::endl;
                 return x;
+            }
 
             // compute initial interval
             // if quadratic part is strictly positive we can compute one bound from the other