Update admin.py

Improvements on _patch_prepopulated_fields
Make every manager MultiLingual, not only objects (close #198).
Use ugettext_lazy instead of ugettext (close #202).
Merge remote branch.

Fix _patch_prepopulated_fields (close #190, #181).
Don't import individual settings.
Add more prepopulated_fields tests.
Clarify docs about fallback usage (close #182).
Update docs about manager patching.
Fix compatibility with older jQuery.
Show None checkboxes on form fields, especially admin (close #187).
Fix form handling in case of excluded translated field (close #183).
Fix test running under Postgres.
Update Changelog.
Use Django 1.6 for travis instead of Django master.
Try to fix Postgres transaction errors in Django 1.5.
Remove tabindex on ClearableWidgetWrapper.
Make ClearableWidgetWrapper compatible with Django 1.6 (_has_changed).
Add OneToOneField support.
Add caching test for relation fields.
Make loaddata command retain locale (close #151).