The foreign-key-checking loop in ATRewriteTables failed to ignore
relations without storage (e.g., partitioned tables), unlike the
initial loop.  This accidentally worked as long as RI_Initial_Check
succeeded, which it does in most practical cases (including all the
ones exercised in the existing regression tests :-().  However, if
that failed, as for instance when there are permissions issues,
then we entered the slow fire-the-trigger-on-each-tuple path.
And that would try to read from the referencing relation, and fail
if it lacks storage.

A second problem, recently introduced in HEAD, was that this loop
had been broken by sloppy refactoring for the tableam API changes.

Repair both issues, and add a regression test case so we have some
coverage on this code path.  Back-patch as needed to v11.

(It looks like this code could do with additional bulletproofing,
but let's get a working test case in place first.)

Hadi Moshayedi, Tom Lane, Andres Freund

Discussion: https://postgr.es/m/CAK=1=WrnNmBbe5D9sm3t0a6dnAq3cdbF1vXY816j1wsMqzC8bw@mail.gmail.com
Discussion: https://postgr.es/m/19030.1554574075@sss.pgh.pa.us
Discussion: https://postgr.es/m/20190325180405.jytoehuzkeozggxx%40alap3.anarazel.de