Fix syslogger to not lose log coherency under high load.

The original coding of the syslogger had an arbitrary limit of 20 large
messages concurrently in progress, after which it would just punt and dump
message fragments to the output file separately.  Our ambitions are a bit
higher than that now, so allow the data structure to expand as necessary.

Reported and patched by Andrew Dunstan; some editing by Tom
Remove useless PGRES_COPY_BOTH "support" in psql.

There is no existing or foreseeable case in which psql should see a
PGRES_COPY_BOTH PQresultStatus; and if such a case ever emerges, it's a
pretty good bet that these code fragments wouldn't do the right thing
anyway.  Remove them, and let the existing default cases do the appropriate
thing, namely emit an "unexpected PQresultStatus" bleat.

Noted while working on libpq row processor patch, for which I was
considering adding a PGRES_SUSPENDED status code --- the same default-case
treatment would be appropriate for that.
Add a "row processor" API to libpq for better handling of large results.

Traditionally libpq has collected an entire query result before passing
it back to the application.  That provides a simple and transactional API,
but it's pretty inefficient for large result sets.  This patch allows the
application to process each row on-the-fly instead of accumulating the
rows into the PGresult.  Error recovery becomes a bit more complex, but
often that tradeoff is well worth making.

Kyotaro Horiguchi, reviewed by Marko Kreen and Tom Lane
Improve efficiency of dblink by using libpq's new row processor API.

This patch provides a test case for libpq's row processor API.
contrib/dblink can deal with very large result sets by dumping them into
a tuplestore (which can spill to disk) --- but until now, the intermediate
storage of the query result in a PGresult meant memory bloat for any large
result.  Now we use a row processor to convert the data to tuple form and
dump it directly into the tuplestore.

A limitation is that this only works for plain dblink() queries, not
dblink_send_query() followed by dblink_get_result().  In the latter
case we don't know the desired tuple rowtype soon enough.  While hack
solutions to that are possible, a different user-level API would
probably be a better answer.

Kyotaro Horiguchi, reviewed by Marko Kreen and Tom Lane
Fix plpgsql named-cursor-parameter feature for variable name conflicts.

The parser got confused if a cursor parameter had the same name as
a plpgsql variable.  Reported and diagnosed by Yeb Havinga, though
this isn't exactly his proposed fix.

Also, some mostly-but-not-entirely-cosmetic adjustments to the original
named-cursor-parameter patch, for code readability and better error
diagnostics.
Expose track_iotiming data via the statistics collector.

Ants Aasma's original patch to add timing information for buffer I/O
requests exposed this data at the relation level, which was judged too
costly.  I've here exposed it at the database level instead.
Correctly explain units used by function-timing stats functions.

The views are in milliseconds, but the raw functions return
microseconds.
Update obsolete comment.

Somebody didn't bother to fix this comment while adding foreign table
support to the code below it.

In passing, remove the explicit calling-out of relkind letters, which adds
complexity to the comment but doesn't help in understanding the code.
Publish checkpoint timing information to pg_stat_bgwriter.

Greg Smith, Peter Geoghegan, and Robert Haas
Allow pg_archivecleanup to strip optional file extensions.

Greg Smith and Jaime Casanova, reviewed by Alex Shulgin and myself.
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