Use ereport not elog for some corrupt-HOT-chain reports.

Use ereport not elog for some corrupt-HOT-chain reports.

These errors have been seen in the field in corrupted-data situations.
It seems worthwhile to report them with ERRCODE_DATA_CORRUPTED, rather
than the generic ERRCODE_INTERNAL_ERROR, for the benefit of log monitoring
and tools like amcheck.  However, use errmsg_internal so that the text
strings still aren't translated; it seems unlikely to be worth
translators' time to do so.

Back-patch to 9.3, like the predecessor commit d70cf811f that introduced
these elog calls originally (replacing Asserts).

Peter Geoghegan

Discussion: https://postgr.es/m/CAH2-Wzmn4-Pg-UGFwyuyK-wiTih9j32pwg_7T9iwqXpAUZr=Mg@mail.gmail.com