Non-reproducible valgrind failure on HEAD

I happened to be trying to run the core regression tests under
valgrind, and I got the complaints attached below, from the
process that had been running the insert_conflict test script.

I could not reproduce the failure in a second run, which is not
hugely surprising because it appears to be in cross-process
sinval processing; so timing sensitivity is to be expected.
That doesn't make it any less disturbing.

One point worth mentioning is that I'd forgotten to build with
"#define USE_VALGRIND" in the first try. AFAIK that should make
valgrind strictly less sensitive, so I think it's not material,
but still.

Thoughts?

regards, tom lane