Change verbosity level of warning message in transport solver

Don't print message "s was clamped in some cells" unless preprocessor
symbol 'VERBOSE' is set.

opm/core/transport/implicit/SinglePointUpwindTwoPhase.hpp

@@ -577,7 +577,9 @@ namespace Opm {
                 store_.dpc(c)     = dpc;
             }
             if (!in_range) {
+#ifdef VERBOSE
                 std::cout << "Warning: initIteration() - s was clamped in some cells.\n";
+#endif
             }
             return in_range;
         }