fix valgrind test path
fix valgrind test path

springmeyer/mapnik-c-api,fawick/mapnik-c-api,springmeyer/mapnik-c-api,springmeyer/mapnik-c-api,fawick/mapnik-c-api,fawick/mapnik-c-api,springmeyer/mapnik-c-api,fawick/mapnik-c-api,springmeyer/mapnik-c-api,fawick/mapnik-c-api