[HACKERS] recent deadlock regression test failures

Hi,

There's two machines that recently report changes in deadlock detector
output:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2017-04-05%2018%3A58%3A04
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=friarbird&dt=2017-04-07%2004%3A20%3A01

both just failed twice in a row:
https://buildfarm.postgresql.org/cgi-bin/show_history.pl?nm=hyrax&br=HEAD
https://buildfarm.postgresql.org/cgi-bin/show_history.pl?nm=friarbird&br=HEAD
without previous errors of the same ilk.

I don't think any recent changes are supposed to affect deadlock
detector behaviour?

- Andres