Document how to avoid foreign key constraint error after upgrade to 1.8

[Rachel Willmer]

I hit this problem myself, and eventually figured out that it was because I hadn't created the fake install of the initial migrations for all my apps in my Django project.

I've seen and answered a few questions caused by this on StackOverflow, so I suspect it may be a common problem. e.g.

​http://stackoverflow.com/questions/29483119/django-1-8-syncdb-not-working-throwing-a-foreign-key-constraint-error
​http://stackoverflow.com/questions/28561458/django-mysql-error-when-creating-tables

[Rachel Willmer]

Suggested addition to ​https://docs.djangoproject.com/en/1.8/topics/migrations/#adding-migrations-to-apps (and the FAQ?)

Note: If you have upgraded to 1.8 or later from a previous version, and are getting a "Foreign Key constraint" error, check that you have created and fake-applied your initial migrations for all your apps. Without this, the tables will be created in the wrong order, which causes this error.

If you have made no migrations, then you can do this project-wide with:
$ python manage.py make migrations
$ python manage.py migrate --fake-initial

If you have made some, but not all, migrations, then you can do this on each remaining app with:
$ python manage.py make migrations your_app_label
$ python manage.py migrate --fake-initial your_app_label

[Tim Graham]

Ticket isn't marked as fixed until the patch is merged.

[Tim Graham <timograham@…>]

In 70912e13:

Fixed #25168 -- Documented how to avoid foreign key constraint error after upgrading to 1.8.

[Tim Graham <timograham@…>]

In 466950fa:

[1.8.x] Fixed #25168 -- Documented how to avoid foreign key constraint error after upgrading to 1.8.

Backport of 70912e137d5a6b089f35c662115fb758a00d7002 from master