Fix memory leaks in failure paths in buildACLCommands and parseAclItem.

This is currently only cosmetic, since all the call sites just curl up
and die in event of a failure return.  It might be important for some
future use-case, though, and in any case it quiets warnings from the
clang static analyzer (as reported by Anna Zaks).

Josh Kupershmidt
Fix some more bugs in contrib/xml2's xslt_process().

It failed to check for error return from xsltApplyStylesheet(), as reported
by Peter Gagarinov.  (So far as I can tell, libxslt provides no convenient
way to get a useful error message in failure cases.  There might be some
inconvenient way, but considering that this code is deprecated it's hard to
get enthusiastic about putting lots of work into it.  So I just made it say
"failed to apply stylesheet", in line with the existing error checks.)

While looking at the code I also noticed that the string returned by
xsltSaveResultToString was never freed, resulting in a session-lifespan
memory leak.

Back-patch to all supported versions.
Fix bogus handling of control characters in json_lex_string().

The original coding misbehaved if "char" is signed, and also made the
extremely poor decision to print control characters literally when trying
to complain about them.  Report and patch by Shigeru Hanada.

In passing, also fix core dump risk in report_parse_error() should the
parse state be something other than what it expects.
Add example of archive_command to use with pg_receivexlog
Fix typo

Noted by Erik Rijkers
Use strerror(errno) instead of %m

Found by Fujii Masao
Fix more crash-safe visibility map bugs, and improve comments.

In lazy_scan_heap, we could issue bogus warnings about incorrect
information in the visibility map, because we checked the visibility
map bit before locking the heap page, creating a race condition.  Fix
by rechecking the visibility map bit before we complain.  Rejigger
some related logic so that we rely on the possibly-outdated
all_visible_according_to_vm value as little as possible.

In heap_multi_insert, it's not safe to clear the visibility map bit
before beginning the critical section.  The visibility map is not
crash-safe unless we treat clearing the bit as a critical operation.
Specifically, if the transaction were to error out after we set the
bit and before entering the critical section, we could end up writing
the heap page to disk (with the bit cleared) and crashing before the
visibility map page made it to disk.  That would be bad.  heap_insert
has this correct, but somehow the order of operations got rearranged
when heap_multi_insert was added.

Also, add some more comments to visibilitymap_test, lazy_scan_heap,
and IndexOnlyNext, expounding on concurrency issues.

Per extensive code review by Andres Freund, and further review by Tom
Lane, who also made the original report about the bogus warnings.
Wake WALSender to reduce data loss at failover for async commit.
WALSender now woken up after each background flush by WALwriter, avoiding
multi-second replication delay for an all-async commit workload.
Replication delay reduced from 7s with default settings to 200ms and often
much less, allowing significantly reduced data loss at failover.

Andres Freund and Simon Riggs
Do unlocked prechecks in bufmgr.c loops that scan the whole buffer pool.

DropRelFileNodeBuffers, DropDatabaseBuffers, FlushRelationBuffers, and
FlushDatabaseBuffers have to scan the whole shared_buffers pool because
we have no index structure that would find the target buffers any more
efficiently than that.  This gets expensive with large NBuffers.  We can
shave some cycles from these loops by prechecking to see if the current
buffer is interesting before we acquire the buffer header lock.
Ordinarily such a test would be unsafe, but in these cases it should be
safe because we are already assuming that the caller holds a lock that
prevents any new target pages from being loaded into the buffer pool
concurrently.  Therefore, no buffer tag should be changing to a value of
interest, only away from a value of interest.  So a false negative match
is impossible, while a false positive is safe because we'll recheck after
acquiring the buffer lock.  Initial testing says that this speeds these
loops by a factor of 2X to 3X on common Intel hardware.

Patch for DropRelFileNodeBuffers by Jeff Janes (based on an idea of
Heikki's); extended to the remaining sequential scans by Tom Lane
Message style improvements
Documentation spell and markup checking
Scan the buffer pool just once, not once per fork, during relation drop.

This provides a speedup of about 4X when NBuffers is large enough.
There is also a useful reduction in sinval traffic, since we
only do CacheInvalidateSmgr() once not once per fork.

Simon Riggs, reviewed and somewhat revised by Tom Lane
Documentation style improvements
When using libpq URI syntax, error out on invalid parameter names.

Dan Farina
Fix bug in early startup of Hot Standby with subtransactions.
When HS startup is deferred because of overflowed subtransactions, ensure
that we re-initialize KnownAssignedXids for when both existing and incoming
snapshots have non-zero qualifying xids.

Fixes bug #6661 reported by Valentine Gogichashvili.

Analysis and fix by Andres Freund
Add ERROR msg for GLOBAL/LOCAL TEMP is not yet implemented
Revert error message on GLOBAL/LOCAL pending further discussion
Make include files work without having to include other ones first
Error message capitalization fix
Fix pg_basebackup/pg_receivexlog for floating point timestamps

Since the replication protocol deals with TimestampTz, we need to
care for the floating point case as well in the frontend tools.

Fujii Masao, with changes from Magnus Hagander