Fixed #15932 - Documented how to supress multiple reverse relations to the same model.

Thanks Claude Paroz for the patch.

docs/ref/models/fields.txt

@@ -1002,9 +1002,10 @@ define the details of how the relation works.
     <abstract-base-classes>`; and when you do so
     :ref:`some special syntax <abstract-related-name>` is available.
 
-    If you'd prefer Django didn't create a backwards relation, set ``related_name``
-    to ``'+'``. For example, this will ensure that the ``User`` model won't get a
-    backwards relation to this model::
+    If you'd prefer Django not to create a backwards relation, set
+    ``related_name`` to ``'+'`` or end it with ``'+'``. For example, this will
+    ensure that the ``User`` model won't have a backwards relation to this
+    model::
 
         user = models.ForeignKey(User, related_name='+')
 
@@ -1095,6 +1096,13 @@ that control how the relationship functions.
 
     Same as :attr:`ForeignKey.related_name`.
 
+    If you have more than one ``ManyToManyField`` pointing to the same model
+    and want to suppress the backwards relations, set each ``related_name``
+    to a unique value ending with ``'+'``::
+
+        users = models.ManyToManyField(User, related_name='u+')
+        referents = models.ManyToManyField(User, related_name='ref+')
+
 .. attribute:: ManyToManyField.limit_choices_to
 
     Same as :attr:`ForeignKey.limit_choices_to`.