Otherwise, partitioned tables with RETURNING expressions or subject
to a WITH CHECK OPTION do not work properly.

Amit Langote, reviewed by Amit Khandekar and Etsuro Fujita.  A few
comment changes by me.

Discussion: http://postgr.es/m/9a39df80-871e-6212-0684-f93c83be4097@lab.ntt.co.jp