Incompatibility with django.forms: Django's CheckboxInput always returns bool

[gregmuellegger]

floppyforms' CheckboxInput returns the value given in the <input value="..."> attribute, but Django always casts this value to a bool, see here: https://github.com/django/django/blob/1.8/django/forms/widgets.py#L495

We should make the behaviour the same as Django's.