[1.7.x] Fixed #22747 -- Add backwards compatibility tip for new behavior of formset.save(commit=False).

Thanks django at patjack.co.uk.

Backport of 2f7a7842ba from master

docs/topics/forms/formsets.txt

@@ -523,6 +523,18 @@ model instances for deleted forms will be deleted when you call
         >>> for obj in formset.deleted_objects:
         ...     obj.delete()
 
+    If you want to maintain backwards compatibility with Django 1.6 and earlier,
+    you can do something like this::
+
+        >>> try:
+        >>>     # For Django 1.7+
+        >>>     for obj in formset.deleted_objects:
+        >>>         obj.delete()
+        >>> except AssertionError:
+        >>>     # Django 1.6 and earlier already deletes the objects, trying to
+        >>>     # delete them a second time raises an AssertionError.
+        >>>     pass
+
 On the other hand, if you are using a plain ``FormSet``, it's up to you to
 handle ``formset.deleted_forms``, perhaps in your formset's ``save()`` method,
 as there's no general notion of what it means to delete a form.