Copy-editing of row security

Address a few typos in the row security update, pointed out
off-list by Adam Brightwell.  Also include 'ALL' in the list
of commands supported, for completeness.
Add -D option to specify data directory to pg_controldata and pg_resetxlog.

It was confusing that to other commands, like initdb and postgres, you would
pass the data directory with "-D datadir", but pg_controldata and
pg_resetxlog would take just plain path, without the "-D". With this patch,
pg_controldata and pg_resetxlog also accept "-D datadir".

Abhijit Menon-Sen, with minor kibitzing by me
Return NULL from json_object_agg if it gets no rows.

This makes it consistent with the docs and with all other builtin
aggregates apart from count().
Fix VPATH builds of the replication parser from git for some !gcc compilers.

Some compilers don't automatically search the current directory for
included files. 9cc2c182fc2 fixed that for builds from tarballs by
adding an include to the source directory. But that doesn't work when
the scanner is generated in the VPATH directory. Use the same search
path as the other parsers in the tree.

One compiler that definitely was affected is solaris' sun cc.

Backpatch to 9.1 which introduced using an actual parser for
replication commands.
Refactor space allocation for base64 encoding/decoding in pgcrypto.

Instead of trying to accurately calculate the space needed, use a StringInfo
that's enlarged as needed. This is just moving things around currently - the
old code was not wrong - but this is in preparation for a patch that adds
support for extra armor headers, and would make the space calculation more
complicated.

Marko Tiikkaja
Change locking regimen around buffer replacement.

Previously, we used an lwlock that was held from the time we began
seeking a candidate buffer until the time when we found and pinned
one, which is disastrous for concurrency.  Instead, use a spinlock
which is held just long enough to pop the freelist or advance the
clock sweep hand, and then released.  If we need to advance the clock
sweep further, we reacquire the spinlock once per buffer.

This represents a significant increase in atomic operations around
buffer eviction, but it still wins on many workloads.  On others, it
may result in no gain, or even cause a regression, unless the number
of buffer mapping locks is also increased.  However, that seems like
material for a separate commit.  We may also need to consider other
methods of mitigating contention on this spinlock, such as splitting
it into multiple locks or jumping the clock sweep hand more than one
buffer at a time, but those, too, seem like separate improvements.

Patch by me, inspired by a much larger patch from Amit Kapila.
Reviewed by Andres Freund.
Remove ill-conceived ban on zero length json object keys.

We removed a similar ban on this in json_object recently, but the ban in
datum_to_json was left, which generate4d sprutious errors in othee json
generators, notable json_build_object.

Along the way, add an assertion that datum_to_json is not passed a null
key. All current callers comply with this rule, but the assertion will
catch any possible future misbehaviour.
Add a basic atomic ops API abstracting away platform/architecture details.

Several upcoming performance/scalability improvements require atomic
operations. This new API avoids the need to splatter compiler and
architecture dependent code over all the locations employing atomic
ops.

For several of the potential usages it'd be problematic to maintain
both, a atomics using implementation and one using spinlocks or
similar. In all likelihood one of the implementations would not get
tested regularly under concurrency. To avoid that scenario the new API
provides a automatic fallback of atomic operations to spinlocks. All
properties of atomic operations are maintained. This fallback -
obviously - isn't as fast as just using atomic ops, but it's not bad
either. For one of the future users the atomics ontop spinlocks
implementation was actually slightly faster than the old purely
spinlock using implementation. That's important because it reduces the
fear of regressing older platforms when improving the scalability for
new ones.

The API, loosely modeled after the C11 atomics support, currently
provides 'atomic flags' and 32 bit unsigned integers. If the platform
efficiently supports atomic 64 bit unsigned integers those are also
provided.

To implement atomics support for a platform/architecture/compiler for
a type of atomics 32bit compare and exchange needs to be
implemented. If available and more efficient native support for flags,
32 bit atomic addition, and corresponding 64 bit operations may also
be provided. Additional useful atomic operations are implemented
generically ontop of these.

The implementation for various versions of gcc, msvc and sun studio have
been tested. Additional existing stub implementations for
* Intel icc
* HUPX acc
* IBM xlc
are included but have never been tested. These will likely require
fixes based on buildfarm and user feedback.

As atomic operations also require barriers for some operations the
existing barrier support has been moved into the atomics code.

Author: Andres Freund with contributions from Oskari Saarenmaa
Reviewed-By: Amit Kapila, Robert Haas, Heikki Linnakangas and Álvaro Herrera
Discussion: CA+TgmoYBW+ux5-8Ja=Mcyuy8=VXAnVRHp3Kess6Pn3DMXAPAEA@mail.gmail.com,
    20131015123303.GH5300@awork2.anarazel.de,
    20131028205522.GI20248@awork2.anarazel.de
Fix atomic ops for x86 gcc compilers that don't understand atomic intrinsics.

Per buildfarm animal locust.
Fix atomic ops inline x86 inline assembly for older 32bit gccs.

Some x86 32bit versions of gcc apparently generate references to the
nonexistant %sil register when using when using the r input
constraint, but not with the =q constraint. The latter restricts
allocations to a/b/c/d which should all work.
Define META_FREE in a way that doesn't cause -Wempty-body warnings.

That get rids of the only -Wempty-body warning when compiling postgres
with gcc 4.8/9. As 6550b901f shows, it's useful to be able to use that
option routinely.

Without asserts there's many more warnings, but that's food for
another commit.
Fix whitespace
Fix a couple occurrences of 'the the' in the new atomics API.

Author: Erik Rijkers
Further atomic ops portability improvements and bug fixes.

* Don't play tricks for a more efficient pg_atomic_clear_flag() in the
  generic gcc implementation. The old version was broken on gcc < 4.7
  on !x86 platforms. Per buildfarm member chipmunk.
* Make usage of __atomic() fences depend on HAVE_GCC__ATOMIC_INT32_CAS
  instead of HAVE_GCC__ATOMIC_INT64_CAS - there's platforms with 32bit
  support that don't support 64bit atomics.
* Blindly fix two superflous #endif in generic-xlc.h
* Check for --disable-atomics in platforms but x86.
Fix identify_locking_dependencies for schema-only dumps.

Without this fix, parallel restore of a schema-only dump can deadlock,
because when the dump is schema-only, the dependency will still be
pointing at the TABLE item rather than the TABLE DATA item.

Robert Haas and Tom Lane
Fix relcache for policies, and doc updates

Andres pointed out that there was an extra ';' in equalPolicies, which
made me realize that my prior testing with CLOBBER_CACHE_ALWAYS was
insufficient (it didn't always catch the issue, just most of the time).
Thanks to that, a different issue was discovered, specifically in
equalRSDescs.  This change corrects eqaulRSDescs to return 'true' once
all policies have been confirmed logically identical.  After stepping
through both functions to ensure correct behavior, I ran this for
about 12 hours of CLOBBER_CACHE_ALWAYS runs of the regression tests
with no failures.

In addition, correct a few typos in the documentation which were pointed
out by Thom Brown (thanks!) and improve the policy documentation further
by adding a flushed out usage example based on a unix passwd file.

Lastly, clean up a few comments in the regression tests and pg_dump.h.