libpq: Fix a few bits that didn't get the memo about COPY BOTH.

There's probably no real bug here at present, so not backpatching.
But it seems good to make these bits consistent with the rest of
libpq, so as to avoid future surprises.

Patch by me.  Review by Tom Lane.
Ensure that user created rows in extension tables get dumped if the table is explicitly requested, either with a -t/--table switch of the table itself, or by -n/--schema switch of the schema containing the extension table. Patch reviewed by Vibhor Kumar and Dimitri Fontaine.

Backpatched to 9.1 when the extension management facility was added.
Fix collation assignment for aggregates with ORDER BY.

ORDER BY expressions were being treated the same as regular aggregate
arguments for purposes of collation determination, but really they should
not affect the aggregate's collation at all; only collations of the
aggregate's regular arguments should affect it.

In many cases this mistake would lead to incorrectly throwing a "collation
conflict" error; but in some cases the corrected code will silently assign
a different collation to the aggregate than before, for example
	agg(foo ORDER BY bar COLLATE "x")
which will now use foo's collation rather than "x" for the aggregate.
Given this risk and the lack of field complaints about the issue, it
doesn't seem prudent to back-patch.

In passing, rearrange code in assign_collations_walker so that we don't
need multiple copies of the standard logic for computing collation of a
node with children.  (Previously, CaseExpr duplicated the standard logic,
and we would have needed a third copy for Aggref without this change.)

Andrew Gierth and David Fetter
Update config.guess and config.sub
Improve message about failed transaction log archiving

The old phrasing appeared to imply that the failure was terminal.
Improve that by indicating that archiving will be tried again later.