Mostly in the new subscription-related commands. Backport the few that
were also present in older versions.

Thomas Munro

Discussion: https://www.postgresql.org/message-id/CAEepm=3CyW1QmXcXJXmqiJXtXzFDc8SvSfnxkEGD3Bkv2SrkeQ@mail.gmail.com