Fixed #26231 -- Used .get_username in admin login template.

django/contrib/admin/templates/admin/login.html

@@ -34,7 +34,7 @@
 
 {% if user.is_authenticated %}
 <p class="errornote">
-{% blocktrans with username=request.user.username trimmed %}
+{% blocktrans with username=request.user.get_username trimmed %}
     You are authenticated as {{ username }}, but are not authorized to
     access this page. Would you like to login to a different account?
 {% endblocktrans %}

docs/releases/1.9.3.txt

@@ -42,3 +42,7 @@ Bugfixes
   regressed in Django 1.9 (:ticket:`26253`).
 
 * Fixed ``BoundField`` to reallow slices of subwidgets (:ticket:`26267`).
+
+* Changed the admin's "permission denied" message in the login template to use
+  ``get_username`` instead of ``username`` to support custom user models
+  (:ticket:`26231`).