Add schema evolution compatibility for Django 1.7, 1.8, and 1.9.
Review Request #8549 — Created Nov. 21, 2016 and discarded
This updates the compatibility modules in Django Evolution to support Django 1.7 through 1.9. These make use of the new Schema Editor functionality introduced with Django 1.7's migration feature to generate SQL equivalent to what these versions of Django would generate, helping us to stay compatible in the future. Not all of the Schema Editor support is public, and not all of the logic we need is even accessible, so we are forced to access private functions and re-implement logic here and there, but generally, it's pretty reasonable. Each of the newly-supported versions of Django generate SQL differently from older versions, and differently from each other. In some cases, these are enough where we have to actually compare against sample SQL datasets specific to certain versions of Django. This change is not sufficient to actually enable evolution for a project. It just brings API compatibility. The work to make evolutions and migrations work together will be a whole separate project. Testing Done: Unit tests pass against Django 1.6, 1.7, 1.8, and 1.9 for SQLite, MySQL, and Postgres. Reviewed at https://reviews.reviewboard.org/r/8109/