Event triggers + table partitioning cause server crash in current master

Hackers,

I discovered a reproducible crash using event triggers in the current
development version, 29c7d5e4844443acaa74a0d06dd6c70b320bb315.
I was getting a crash before this version, and cloned a fresh copy of
the sources to be sure I was up to date, so I don't think the bug can be
attributed to Andres' commit. (The prior version I was testing against
was heavily modified by me, so I recreated the bug using the latest
standard, unmodified sources.)

I create both before and after event triggers early in the regression test
schedule, which then fire here and there during the following tests, leading
fairly reproducibly to the server crashing somewhere during the test suite.
These crashes do not happen for me without the event triggers being added
to the tests. Many tests show as 'FAILED' simply because the logging
that happens in the event triggers creates unexpected output for the test.
Those "failures" are expected. The server crashes are not.

The server logs suggest the crashes might be related to partitioned tables.

Please find attached the patch that includes my changes to the sources
for recreating this bug. The logs and regression.diffs are a bit large; let
me know if you need them.

I built using the command

./configure --enable-cassert --enable-tap-tests && make -j4 && make check

Mark Dilger