During parallel pg_dump, free commands from master

The command strings read by the child processes during parallel
pg_dump, after being read and handled, were not being free'd.
This patch corrects this relatively minor memory leak.

Leak found by the Coverity scanner.

Back patch to 9.3 where parallel pg_dump was introduced.
pg_receivexlog - Exit on failure to parse

In streamutil.c:GetConnection(), upgrade failure to parse the
connection string to an exit(1) instead of simply returning NULL.
Most callers already immediately exited, but pg_receivexlog would
loop on this case, continually trying to re-parse the connection
string (which can't be changed after pg_receivexlog has started).

GetConnection() was already expected to exit(1) in some cases
(eg: failure to allocate memory or if unable to determine the
integer_datetimes flag), so this change shouldn't surprise anyone.

Began looking at this due to the Coverity scanner complaining that
we were leaking err_msg in this case- no longer an issue since we
just exit(1) immediately.
pg_isready: Message improvement
Ensure 64bit arithmetic when calculating tapeSpace

In tuplesort.c:inittapes(), we calculate tapeSpace by first figuring
out how many 'tapes' we can use (maxTapes) and then multiplying the
result by the tape buffer overhead for each.  Unfortunately, when
we are on a system with an 8-byte long, we allow work_mem to be
larger than 2GB and that allows maxTapes to be large enough that the
32bit arithmetic can overflow when multiplied against the buffer
overhead.

When this overflow happens, we end up adding the overflow to the
amount of space available, causing the amount of memory allocated to
be larger than work_mem.

Note that to reach this point, you have to set work mem to at least
24GB and be sorting a set which is at least that size.  Given that a
user who can set work_mem to 24GB could also set it even higher, if
they were looking to run the system out of memory, this isn't
considered a security issue.

This overflow risk was found by the Coverity scanner.

Back-patch to all supported branches, as this issue has existed
since before 8.4.
Be sure to close() file descriptor on error case

In receivelog.c:writeTimeLineHistoryFile(), we were not properly
closing the open'd file descriptor in error cases.  While this
wouldn't matter much if we were about to exit due to such an
error, that's not the case with pg_receivexlog as it can be a
long-running process and these errors are non-fatal.

This resource leak was found by the Coverity scanner.

Back-patch to 9.3 where this issue first appeared.
Fix resource leak in initdb -X option

When creating the symlink for the xlog directory, free the string
which stores the link location.  Not really an issue but it doesn't
hurt to be good about this- prior cleanups have fixed similar
issues.

Leak found by the Coverity scanner.

Not back-patching as I don't see it being worth the code churn.
Document the OVER keyword as being unreserved.

It became so in commit 5893ffa79c03824f34ae3d37f211381fd1c17283.

David Fetter, extracted from a larger patch.
Check version before allocating PQExpBuffer

In pg_dump.c:getEventTriggers, check what major version we are on
before calling createPQExpBuffer() to avoid leaking that bit of
memory.

Leak discovered by the Coverity scanner.

Back-patch to 9.3 where support for dumping event triggers was
added.