It's better to use the actual keynum here rather than 0, because
someday someone might try to make list partitioning work with
multiple partitioning columns.

Jeevan Ladhe

Discussion: http://postgr.es/m/CAOgcT0M6-mx+dSX47JGJuJP1CKr4XssBFVmKNETt0OZYWpFr+w@mail.gmail.com