[PATCH] Reserve protocol 3.1 explicitly in pqcomm.h - Mailing list pgsql-hackers

Hi,

This is a tiny followup to https://postgr.es/c/0664aa4ff8 that
enshrines the unused 3.1 protocol version as PG_PROTOCOL_RSRV31. The
patch comes from [1]; I just wanted to give people the opportunity to
bikeshed the name (or object to the move?) before it becomes part of a
public header.

Thanks,
--Jacob

[1] https://postgr.es/m/CAOYmi%2B%3DPMq5wiKjBuOF2_W6JYRnPFYbgp7P-MRa2ymFo89%3D6BQ%40mail.gmail.com