Fix widgets rendering

[artscoop]

Some widgets only take into input unicode strings (when coming from POST data), whereas they can output str strings (in Python 2.7, DatetimeWidget.data_from_value_dict uses datetime.datetime.strftime which returns a str (not unicode). This value is ignored in DatetimeWidget.render because it's not a unicode - and should not have to) So the functionality was broken only in Python 2.7. Replaced six.text_type (unicode in 2.7 and str in 3.3) with six.string_types (basestring in 2.7 and str in 3.3)

[gregmuellegger]

I just released django-floppyforms 1.4.0 which contains your changes. Thanks for your work! https://pypi.python.org/pypi/django-floppyforms/