BooleanField.default=False in PublishingMixin.

This is to account for a change in behaviour in Django 1.6. See
https://docs.djangoproject.com/en/1.6/ref/models/fields/#booleanfield
for more information.

The South migrations of other apps using this mixin confirm that False
was the intended deault.
BooleanField.default=False for EnabledField.

This is to account for a change in behaviour in Django 1.6. See
https://docs.djangoproject.com/en/1.6/ref/models/fields/#booleanfield
for more information.