Fixed #25160 (again) -- Moved data loss check on reverse relations.

Moved data loss check when assigning to a reverse one-to-one relation on
an unsaved instance to Model.save(). This is exactly the same change as
e4b813c but for reverse relations.

docs/releases/1.8.5.txt

@@ -39,3 +39,7 @@ Bugfixes
 
 * Fixed custom queryset chaining with ``values()`` and ``values_list()``
   (:ticket:`20625`).
+
+* Moved the :ref:`unsaved model instance assignment data loss check
+  <unsaved-model-instance-check-18>` on reverse relations to ``Model.save()``
+  (:ticket:`25160`).

docs/releases/1.8.txt

@@ -702,6 +702,9 @@ Assigning unsaved objects to relations raises an error
         ...
         ValueError: save() prohibited to prevent data loss due to unsaved related object 'author'.
 
+    A similar check on assignment to reverse one-to-one relations was removed
+    in Django 1.8.5.
+
 Assigning unsaved objects to a :class:`~django.db.models.ForeignKey`,
 :class:`~django.contrib.contenttypes.fields.GenericForeignKey`, and
 :class:`~django.db.models.OneToOneField` now raises a :exc:`ValueError`.