Uploading patch with minor test changes (dbm_bool_b.patch).

Backwards compatibility note:

Result of running bool(db) on a db that has been closed:
  Old: _dbm.error: DBM object has already been closed
  With patch: returns False instead of raising.

I think this is desireable, but we could have bool(db) raise an exception when the db is closed if that is preferred for backwards compatibility.