Log Message:
Changes 1.8.1:
- Slovak translation (@jbub).
- Deleting a user no longer deletes the associated revisions (@daaray).
- Improving handling of inline models in admin integration (@blueyed).
- Improving error messages for proxy model registration (@blueyed).
- Improvements to using migrations with custom user model (@aivins).
- Removing sys.exit() in deleterevisions management command, allowing it to be \ 
used internally by Django projects (@tongwang).
- Fixing some backwards-compatible admin deprecation warnings (Thomas Schreiber).
- Fixing tests if RevisionMiddleware is used as a decorator in the parent \ 
project (@jmoldow).
- Derived models, such as those generated by deferred querysets, now work.
- Removed deprecated low-level API methods.