RE: [PoC] pg_upgrade: allow to upgrade publisher node

Dear Peter,

> A suggestion: You could write some/most tests against test_decoding
> rather than the publication/subscription system. That way, you can
> avoid many timing issues in the tests and you can check more exactly
> that the slots produce the output you want. This would also help ensure
> that this new facility works for other logical decoding output plugins
> besides the built-in one.

Good point. I think almost tests except --check part can be rewritten.
PSA new patchset.

Additionally, I fixed followings:

- Added initialization for slot_arr.*. This is needed to check whether
the entry has already been allocated, in get_logical_slot_infos().
Previously double-free was occurred in some platform.
- fixed condition in get_logical_slot_infos()
- Changed the expected size of page header to longer one(SizeOfXLogLongPHD).
If the WAL page is the first one in the WAL segment file, the long header seems
to be used.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED