Preserve versions of initdb-created collations in pg_upgrade

As mentioned in [0], pg_upgrade currently does not preserve the version
of collation objects created by initdb. Here is an attempt to fix that.

The way I deal with this here is by having the binary-upgrade mode in
pg_dump delete all the collations created by initdb and then dump out
CREATE COLLATION commands with version information normally.

I had originally imagined doing some kind of ALTER COLLATION (or perhaps
a direct UPDATE pg_collation) to update the version information, but
that doesn't really work because we don't know whether the collation
object with a given name in the new cluster is the same as the one in
the old cluster. So it seems more robust to just delete all existing
collations and create them from scratch.

Thoughts?

[0]:
https://www.postgresql.org/message-id/CA+hUKGKDe98DFWKJoS7e4Z+Oamzc-1sZfpL3V3PPgi1uNvQ1tw@mail.gmail.com
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services