- The Boolean type, when used on a backend that doesn't

- The Boolean type, when used on a backend that doesn't
have native boolean support, will generate a CHECK
constraint "col IN (0, 1)" along with the int/smallint-
based column type.  This can be switched off if
desired with create_constraint=False.
Note that MySQL has no native boolean *or* CHECK constraint
support so this feature isn't available on that platform.
[ticket:1589]