This improves the admin fieldset rendering in a few important ways:


It splits out the field rendering into its own reusable template

   (admin/includes/field.html).


It adds a unique row ID for each form row in the fieldset, so that

   a field's rows can be referenced.


It wraps template rendering into a ChangeFormFieldset.render()

   method, which can be called by a {% render_change_form_fieldset %}

   template tag. This allows for the next benefit:


The admin/includes/fieldset.html template can now be extended and

   its new fields block overridden. The template can be provided

   by setting the fieldset_template_name attribute on a ModelAdmin.


These will allow pages like the repository configuration page to more

easily specialize certain fieldsets.

Unit tests passed.
Tested along with the other changes to the repository configuration

page.