Fixed #25100 -- Documented an upgrade caveat for contenttypes migration.

  has been removed by a migration and replaced by a property. That means it's

  not possible to query or filter a ``ContentType`` by this field any longer.

  Be careful if you upgrade to Django 1.8 and skip Django 1.7. If you run

  ``manage.py migrate --fake``, this migration will be skipped and you'll see

  a ``RuntimeError: Error creating new content types.`` exception because the

  ``name`` column won't be dropped from the database. Use ``migrate.py migrate

  --fake-initial`` to fake only the initial migration instead.

* :djadmin:`migrate` now accepts the :djadminopt:`--fake-initial` option to

  allow faking initial migrations. In 1.7 initial migrations were always

  automatically faked if all tables created in an initial migration already