BaseAuthBackend (formerly AuthBackend) has been around a long time,

and has gained some cruft over the years, in the forms of capability

flags that Django no longer needs to functions that don't have the most

clear names.
Those capability flags have now been removed, and the methods have been

renamed and made expandable through the introduction of **kwargs.

query_users() has been renamed to populate_users(), and

search_users() has been renamed to build_search_users_query(). These

better reflect the purposes of the methods.
Both renamed methods will look for the legacy versions and, if found,

call them and warn, helping the third-party backends that use these

features in their migration efforts.

Unit tests pass.