Change the way pg_basebackup's tablespace mapping is implemented.

Previously, we would first create the symlinks the way they are in the
original system, and at the end replace them with the mapped symlinks.
That never really made much sense, so now we create the symlink pointing
to the correct location to begin with, so that there's no need to fix
them at the end.

The old coding didn't work correctly on Windows, because Windows junction
points look more like directories than files, and ought to be removed with
rmdir rather than unlink. Also, it incorrectly used "%d" rather than "%u"
to print an Oid, but that's gone now.

Report and patch by Amit Kapila, with minor changes by me. Reviewed by
MauMau. Backpatch to 9.4, where the --tablespace feature was added.
Fix comment in pg_basebackup.

The option is called --tablespace-mapping, not --tablespace.

Amit Kapila
Fix newly introduced misspelling of existence in pg_buffercache.

Peter Geoghegan
Fix corner-case behaviors in JSON/JSONB field extraction operators.

Cause the path extraction operators to return their lefthand input,
not NULL, if the path array has no elements.  This seems more consistent
since the case ought to correspond to applying the simple extraction
operator (->) zero times.

Cause other corner cases in field/element/path extraction to return NULL
rather than failing.  This behavior is arguably more useful than throwing
an error, since it allows an expression index using these operators to be
built even when not all values in the column are suitable for the
extraction being indexed.  Moreover, we already had multiple
inconsistencies between the path extraction operators and the simple
extraction operators, as well as inconsistencies between the JSON and
JSONB code paths.  Adopt a uniform rule of returning NULL rather than
throwing an error when the JSON input does not have a structure that
permits the request to be satisfied.

Back-patch to 9.4.  Update the release notes to list this as a behavior
change since 9.3.
Fix outdated comment
Implement ALTER TABLE .. SET LOGGED / UNLOGGED

This enables changing permanent (logged) tables to unlogged and
vice-versa.

(Docs for ALTER TABLE / SET TABLESPACE got shuffled in an order that
hopefully makes more sense than the original.)

Author: Fabrízio de Royes Mello
Reviewed by: Christoph Berg, Andres Freund, Thom Brown
Some tweaking by Álvaro Herrera
doc: Improve pg_restore help output

Add a note that some options can be specified multiple times to select
multiple objects to restore.  This replaces the somewhat confusing use
of plurals in the option descriptions themselves.
Fix another ancient memory-leak bug in relcache.c.

CheckConstraintFetch() leaked a cstring in the caller's context for each
CHECK constraint expression it copied into the relcache.  Ordinarily that
isn't problematic, but it can be during CLOBBER_CACHE testing because so
many reloads can happen during a single query; so complicate the code
slightly to allow freeing the cstring after use.  Per testing on buildfarm
member barnacle.

This is exactly like the leak fixed in AttrDefaultFetch() by commit
078b2ed291c758e7125d72c3a235f128d40a232b.  (Yes, this time I did look for
other instances of the same coding pattern :-(.)  Like that patch, no
back-patch, since it seems unlikely that there's any problem except under
very artificial test conditions.

BTW, it strikes me that both of these places would require further work
comparable to commit ab8c84db2f7af008151b848cf1d6a4672a39eecd, if we ever
supported defaults or check constraints on system catalogs: they both
assume they are copying into an empty relcache data structure, and that
conceivably wouldn't be the case during recursive reloading of a system
catalog.  This does not seem worth worrying about for the moment, since
there is no near-term prospect of supporting any such thing.  So I'll
just note the possibility for the archives' sake.
Don't track DEALLOCATE in pg_stat_statements.

We also don't track PREPARE, nor do we track planning time in general, so
let's ignore DEALLOCATE as well for consistency.

Backpatch to 9.4, but not further than that. Although it seems unlikely that
anyone is relying on the current behavior, this is a behavioral change.

Fabien Coelho
Fix typos in some error messages thrown by extension scripts when fed to psql.

Some of the many error messages introduced in 458857cc missed 'FROM
unpackaged'. Also e016b724 and 45ffeb7e forgot to quote extension
version numbers.

Backpatch to 9.1, just like 458857cc which introduced the messages. Do
so because the error messages thrown when the wrong command is copy &
pasted aren't easy to understand.
Add regression tests for SELECT FOR UPDATE/SHARE NOWAIT.

Thomas Munro
Editorial review of SET UNLOGGED

Add a succint comment explaining why it's correct to change the
persistence in this way.  Also s/loggedness/persistence/ because native
speakers didn't like the latter term.

Fabrízio and Álvaro
Oops, forgot to "git add" one last change
More psprintf goodness
Have CREATE TABLE AS and REFRESH return an OID

Other DDL commands are already returning the OID, which is required for
future additional event trigger work.  This is merely making these
commands in line with the rest of utility command support.
DefineType: return base type OID, not its array

Event triggers want to know the OID of the interesting object created,
which is the main type.  The array created as part of the operation is
just a subsidiary object which is not of much interest.
Use newly added InvalidCommandId instead of 0

The symbol was added by 71901ab6d; the original code was introduced by
6868ed749.  Development of both overlapped which is why we apparently
failed to notice.

This is a (very slight) behavior change, so I'm not backpatching this to
9.4 for now, even though the symbol does exist there.
Revert XactLockTableWait context setup in conditional multixact wait

There's no point in setting up a context error callback when doing
conditional lock acquisition, because we never actually wait and so the
user wouldn't be able to see the context message anywhere.  In fact,
this is more in line with what ConditionalXactLockTableWait is doing.

Backpatch to 9.4, where this was added.
upgrade docs:  highlight pg_upgrade, warn about globals preservation

Also, remove OID preservation mention, mention non-text dump formats

Backpatch through 9.4
pg_ctl, pg_upgrade:  allow multiple -o/-O options, append them

Report by Pavel Raiskup