[1.9.x] Fixed #25744 -- Corrected reference to User object in auth docs.

Backport of ce4914eab4 from master

docs/topics/auth/customizing.txt

@@ -115,12 +115,12 @@ Either way, ``authenticate`` should check the credentials it gets, and it
 should return a ``User`` object that matches those credentials, if the
 credentials are valid. If they're not valid, it should return ``None``.
 
-The Django admin system is tightly coupled to the Django ``User`` object
-described at the beginning of this document. For now, the best way to deal with
-this is to create a Django ``User`` object for each user that exists for your
-backend (e.g., in your LDAP directory, your external SQL database, etc.) You
-can either write a script to do this in advance, or your ``authenticate``
-method can do it the first time a user logs in.
+The Django admin is tightly coupled to the Django :ref:`User object
+<user-objects>`. The best way to deal with this is to create a Django ``User``
+object for each user that exists for your backend (e.g., in your LDAP
+directory, your external SQL database, etc.) You can either write a script to
+do this in advance, or your ``authenticate`` method can do it the first time a
+user logs in.
 
 Here's an example backend that authenticates against a username and password
 variable defined in your ``settings.py`` file and creates a Django ``User``