Use the catversion to distinguish old/new clusters

This makes 9.3 -> 9.3 upgrades work when they cross the commit that
added persistent multixacts; early 9.3 pg_controldata did not have the
required oldestMultiXact line, and so would fail to upgrade.

per Bruce Momjian
Redefine HEAP_XMAX_IS_LOCKED_ONLY

Tuples marked SELECT FOR UPDATE in a cluster that's later processed by
pg_upgrade would have a different infomask bit pattern than those
produced by 9.3dev; that bit pattern was being seen as "dead" by HEAD
(because they would fail the "is this tuple locked" test, and so the
visibility rules would thing they're updated, even though there's no
HEAP_UPDATED version of them).  In other words, some rows could silently
disappear after pg_upgrade.

With this new definition, those tuples become visible again.

This is breakage resulting from my commit 0ac5ad5134.
pg_upgrade:  detect stale postmaster.pid lock files

If the postmaster.pid lock file exists, try starting/stopping the
cluster to check if the lock file is valid.

Per request from Tom.
Use correct output device for Windows prompts.

This ensures that mapping of non-ascii prompts
to the correct code page occurs.

Bug report and original patch from Alexander Law,
reviewed and reworked by Noah Misch.

Backpatch to all live branches.
Fix SPI documentation for new handling of ExecutorRun's count parameter.

Since 9.0, the count parameter has only limited the number of tuples
actually returned by the executor.  It doesn't affect the behavior of
INSERT/UPDATE/DELETE unless RETURNING is specified, because without
RETURNING, the ModifyTable plan node doesn't return control to execMain.c
for each tuple.  And we only check the limit at the top level.

While this behavioral change was unintentional at the time, discussion of
bug #6572 led us to the conclusion that we prefer the new behavior anyway,
and so we should just adjust the docs to match rather than change the code.
Accordingly, do that.  Back-patch as far as 9.0 so that the docs match the
code in each branch.
doc:  correct sepgsql doc about permission checking of CASCADE

Backpatch to 9.2.

Patch from Kohei KaiGai
doc:  add mention of ssi read anomolies to mvcc docs

From Jeff Davis, modified by Kevin Grittner