Commit a2566508 fixed some issues with
how PartitionDispatch related code handled multi-level partitioned
tables, but didn't add any tests.

Discussion: http://postgr.es/m/CA%2BTgmoZ86v1G%2Bzx9etMiSQaBBvYMKfU-iitqZArSh5z0n8Q4cA%40mail.gmail.com

Amit Langote, per a complaint from me.