[1.6.x] Fixed #20988 -- Added model meta option select_on_save

The option can be used to force pre 1.6 style SELECT on save behaviour.
This is needed in case the database returns zero updated rows even if
there is a matching row in the DB. One such case is PostgreSQL update
trigger that returns NULL.

Reviewed by Tim Graham.

Refs #16649

Backport of e973ee6a98 from master

Conflicts:
	django/db/models/options.py
	tests/basic/tests.py

tests/basic/models.py

@@ -19,6 +19,11 @@ class Article(models.Model):
     def __str__(self):
         return self.headline
 
+class ArticleSelectOnSave(Article):
+    class Meta:
+        proxy = True
+        select_on_save = True
+
 @python_2_unicode_compatible
 class SelfRef(models.Model):
     selfref = models.ForeignKey('self', null=True, blank=True,