Fixed #13941 -- Corrected the way sequence names are reset under Postgres,...

Fixed #13941 -- Corrected the way sequence names are reset under Postgres, especially when generic foreign keys are involved. Thanks to Ales Zoulek for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13449 bcc190cf-cafb-0310-a4f2-bffc1f526a37