Re: Proof of concept: standalone backend with full FE/BE protocol

To my mind, the "create a socket and hope nobody else can get to it"
approach is exactly one of the main things we're trying to avoid here.
If you'll recall, awhile back we had a big discussion about how pg_upgrade
could positively guarantee that nobody messed with the source database
while it was working, and we still don't have a bulletproof guarantee
there.  I would like to fix that by making pg_upgrade use only standalone
backends to talk to the source database, never starting a real postmaster
at all.  But if the standalone-pg_dump mode goes through a socket, we're
back to square one on that concern.