The Djblets siteconfig app builds on the admin change_form.html

template, but changes to that template were made at some point which

were causing problems. Specifically, Django seems to have added the

ability to override that template on a per-app or per-model basis, but

that assumed that it was being rendered from within the admin view,

which inserted an opts into the render context which was the model's

_meta object. This change adds the siteconfig's _meta object in

appropriately so that Django's internal InclusionAdminTag doesn't

explode.

Was able to open various settings pages in the Review Board admin UI

without it exploding.