Install extensions using update scripts (was Re: Remove superuser() checks from pgstattuple)

Andres Freund <andres(at)anarazel(dot)de> writes:
> On September 4, 2016 6:33:30 PM PDT, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I think nearly all of the
>> infrastructure for this is already there in extension.c.

> Yes, it doesn't sound very hard...

I poked at this a bit, and indeed it's not that hard. Attached is a
proposed patch (code-complete, I think, but no docs as yet).
Aside from touching CREATE EXTENSION itself, this modifies the
pg_available_extension_versions view to show versions that are installable
on the basis of update chains. I think pg_extension_update_paths() needs
no changes, though.

Ordinarily I'd be willing to stick this on the queue for the next
commitfest, but it seems like we ought to try to get it pushed now
so that Stephen can make use of the feature for his superuser changes.
Thoughts?

regards, tom lane