Exclude inline admins from being reverted when not followed.

Fixes etianen/django-reversion#222

See https://github.com/etianen/django-reversion/issues/222
Using admin classes own revision manager to accessinge revision data.
Fixed tests with custom User model.
Merge pull request #224 from mireq/master

Tests not compatible with custom User model
Merge pull request #1 from etianen/master

Update