Add tests mistakenly left out of r9397.

>>> f.clean('.002') == Decimal("0.002")

True

>>> f = DecimalField(max_digits=2, decimal_places=2)

>>> f.clean('.01') == Decimal(".01")

True

>>> f.clean('1.1')

Traceback (most recent call last):

...

ValidationError: [u'Ensure that there are no more than 0 digits before the decimal point.']

# DateField ###################################################################

>>> import datetime