[1.6.x] 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.

Backport of b990df1d63 from master

django/db/models/sql/compiler.py

@@ -10,6 +10,7 @@ from django.db.models.sql.constants import (SINGLE, MULTI, ORDER_DIR,
 from django.db.models.sql.datastructures import EmptyResultSet
 from django.db.models.sql.expressions import SQLEvaluator
 from django.db.models.sql.query import get_order_dir, Query
+from django.db.transaction import TransactionManagementError
 from django.db.utils import DatabaseError
 from django.utils import six
 from django.utils.six.moves import zip
@@ -142,6 +143,9 @@ class SQLCompiler(object):
                 result.append('OFFSET %d' % self.query.low_mark)
 
         if self.query.select_for_update and self.connection.features.has_select_for_update:
+            if self.connection.get_autocommit():
+                raise TransactionManagementError("select_for_update cannot be used outside of a transaction.")
+
             # If we've been asked for a NOWAIT query but the backend does not support it,
             # raise a DatabaseError otherwise we could get an unexpected deadlock.
             nowait = self.query.select_for_update_nowait