Commit 3de241db missed to update psql to display foreign keys on
partitioned tables.  Add that.

Reported-by: Amit Langote
Author: Amit Langote
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/a66879e5-636f-d4dd-b4a4-92bdca5a828f@lab.ntt.co.jp