Fixed memory leak in _db_set() (Bug#24497 Valgrind warning: get_one_option)
Don't call net_clear() on COM_QUIT. This avoids a warning from net_clear() after shutdown: "skipped ## bytes from file"
BUG#21428: skipped 9 bytes from file: socket (3)" on "mysqladmin shutdown"
in a distinct mysql-bench repository. Also add a new --benchdir option
to mysql-test-run.pl so the location of the mysql-bench repository can
be specified. The default location is adjacent to the source tree.