ella/ella — pull request #125 by cooncesean (2012-09-17 19:49:10+00:00)
Title: Modified `source` FK fields to SET_NULL on delete

Modified `ella.core.models.Publishable` and `ella.photos.models.Photo` 'source' FK fields to SET_NULL on delete (as opposed to deleting the Publishable/Photo when a Source is deleted).

There are only two `source` foreign keys in the ella codebase and both have been updated in this pull request.

Unit tests accompany these changes.