[1.2.X] Fixed #14246: Modified aggregation_regress tests so that they will...

[1.2.X] Fixed #14246: Modified aggregation_regress tests so that they will pass on a variety (sqlite, Postgres, MySQL/MyISAM) of DBs. 

r13712 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13714 bcc190cf-cafb-0310-a4f2-bffc1f526a37