- Fix bsddb.dbtables: Don't randomly corrupt newly inserted rows by
   picking a rowid string with null bytes in it.  Such rows could not
   later be deleted, modified or individually selected.  Existing
   bsdTableDb databases created with such rows are out of luck.
 - Use mkdtemp for the test_dbtables test database environment and
   clean it up afterwards using shutil.rmtree.