Search field on Admin user list page is broken

[maurizi]

Attempting to use the search field on the Django admin User list page causes an uncaught 500 error:

FieldError: Cannot resolve keyword 'username' into field. Choices are: auth_token, burst_rate, date_joined, email, first_name, groups, id, is_active, is_staff, is_superuser, last_login, last_name, logentry, password, project, sustained_rate, user_permissions, userprofile