Comment 19 for bug 1815665

When preparing the changes I happened to realize that we got mislead by too many open tabs and mails in our discussion. The change with a potential to break data is [1] but not [2].
Therefore our discussion was misleading - for [1] there can be no comparable solution for the "check for the symbol in the extensions" as the setting of client_min_messages could be anywhere.

That said I'll switch back to my suggestion to revert of both:
- [1]: client_min_messages: users of Bionic/Cosmic are either
  a) not affected at all and therefore are fine as-is (majority)
  b) not affected by the problem but have tests/scripts/CI/... that relies on the behavior (we
     don't want to SRU break them)
  b) have a case that is affected, in that case the "user" of client_min_messages that is
     considered broken should be changed.
  Furthermore with that decision we are also in sync with Debian handling the same
- [2]: rb/rbt: fine doing forward (Disco), but not Bionic/Cosmic not breaking ABI of the past in
       an SRU

[1]: https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=c09daa910
[2]: https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=b2e754c14