Fixed #22343 -- Disallowed select_for_update in autocommit mode

The ticket was originally about two failing tests, which are
fixed by putting their queries in transactions.

Thanks Tim Graham for the report, Aymeric Augustin for the fix,
and Simon Charette, Tim Graham & Loïc Bistuer for review.

docs/releases/1.7.txt

@@ -1086,6 +1086,31 @@ Note also that the admin login form has been updated to not contain the
 ``this_is_the_login_form`` field (now unused) and the ``ValidationError`` code
 has been set to the more regular ``invalid_login`` key.
 
+``select_for_update()`` requires a transaction
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Historically, queries that use
+:meth:`~django.db.models.query.QuerySet.select_for_update()` could be
+executed in autocommit mode, outside of a transaction. Before Django
+1.6, Django's automatic transactions mode allowed this to be used to
+lock records until the next write operation. Django 1.6 introduced
+database-level autocommit; since then, execution in such a context
+voids the effect of ``select_for_update()``. It is, therefore, assumed
+now to be an error, and raises an exception.
+
+This change may cause test failures if you use ``select_for_update()``
+in a test class which is a subclass of
+:class:`~django.test.TransactionTestCase` rather than
+:class:`~django.test.TestCase`.  
+
+This change was made because such errors can be caused by including an
+app which expects global transactions (e.g. :setting:`ATOMIC_REQUESTS
+<DATABASE-ATOMIC_REQUESTS>` set to True), or Django's old autocommit
+behavior, in a project which runs without them; and further, such
+errors may manifest as data-corruption bugs.
+
+This was also fixed in Django 1.6.3.
+
 Miscellaneous
 ~~~~~~~~~~~~~