Update per-column ACLs, not only per-table ACL, when changing table owner.

We forgot to modify column ACLs, so privileges were still shown as having
been granted by the old owner.  This meant that neither the new owner nor
a superuser could revoke the now-untraceable-to-table-owner permissions.
Per bug #6350 from Marc Balmer.

This has been wrong since column ACLs were added, so back-patch to 8.4.