When we first built our siteconfig template, which has gone on to become
the base for many of our configuration/form templates, we used a
different version of the fieldset structure than Django did. This makes
it a bit difficult for users who are coming from Django's form and
trying to make it work with these forms.

Our template now uses a new get_fieldsets filter, which normalizes the
fieldset entries, allowing the use of either format. It gives us a good
way to transition to Django's form over time.

Tested with existing configuration forms, and with newer forms containing

Django's style.
Unit tests pass.