When adding a migration on master, I discovered that the new-style
migrations were strongly out of sync; Django wanted to create new
migrations for almost every app. That was surprising given that no model
changes were made since building that set of migrations.

The issue is that they were built with Django 1.7 RC2, and we've since
switchted to RC3. If I'd have to guess, I'd say the following issue is
responsible for it:
2da20379c0

As beta 1 is only a day old and it doesn't cause major headaches, it was
decided that it's easiest to release a new set of migrations. And pray
to the gods of Python that we won't have a similar situation again
before the Django migrations framework stabilises.