[1.1.X] Refs django#12288 -- Clarified that application names must be unique. Thanks to Piotr Czachur for the report.

Backport of r13219 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@13224 bcc190cf-cafb-0310-a4f2-bffc1f526a37

Author: freakboy3742

docs/ref/settings.txt

@@ -589,6 +589,14 @@ installation. Each string should be a full Python path to a Python package that
 contains a Django application, as created by :djadmin:`django-admin.py startapp
 <startapp>`.
 
+.. admonition:: App names must be unique
+
+    The application names (that is, the final dotted part of the
+    path to the module containing ``models.py``) defined in
+    :setting:`INSTALLED_APPS` *must* be unique. For example, you can't
+    include both ``django.contrib.auth`` and ``myproject.auth`` in
+    INSTALLED_APPS.
+
 .. setting:: INTERNAL_IPS
 
 INTERNAL_IPS