Fix formats bug in form.TimeField

Thanks for a most useful package. I encountered an issue in admin forms that include time fields.
When submitting a form that includes a TimeField, an exception is thrown on form.py line 71:
`AttributeError: 'TimeField' object has no attribute 'formats'`

And when populating a value into a TimeField; form.py line 65:
`TypeError: strftime() argument 1 must be string or read-only buffer, not tuple`

My solution here works well enough for my needs but there's probably a better way to handle line 65 than just defaulting to the first item in the list of formats...