Additional regression tests for ALTER OPERATOR FAMILY.

Robins Tharakan, reviewed by Szymon Guz
Use InvalidSnapshot, now SnapshotNow, as the default snapshot.

As far as I can determine, there's no code in the core distribution
that fails to explicitly set the snapshot of a scan or executor
state.  If there is any such code, this will probably cause it to
seg fault; friendlier suggestions were discussed on pgsql-hackers,
but there was no consensus that anything more than this was
needed.

This is another step towards the hoped-for complete removal of
SnapshotNow.
Tweak FOR UPDATE/SHARE error message wording (again)

In commit 0ac5ad5134 I changed some error messages from "FOR
UPDATE/SHARE" to a rather long gobbledygook which nobody liked.  Then,
in commit cb9b66d31 I changed them again, but the alternative chosen
there was deemed suboptimal by Peter Eisentraut, who in message
1373937980.20441.8.camel@vanquo.pezone.net proposed an alternative
involving a dynamically-constructed string based on the actual locking
strength specified in the SQL command.  This patch implements that
suggestion.
Change post-rewriter representation of dropped columns in joinaliasvars.

It's possible to drop a column from an input table of a JOIN clause in a
view, if that column is nowhere actually referenced in the view.  But it
will still be there in the JOIN clause's joinaliasvars list.  We used to
replace such entries with NULL Const nodes, which is handy for generation
of RowExpr expansion of a whole-row reference to the view.  The trouble
with that is that it can't be distinguished from the situation after
subquery pull-up of a constant subquery output expression below the JOIN.
Instead, replace such joinaliasvars with null pointers (empty expression
trees), which can't be confused with pulled-up expressions.  expandRTE()
still emits the old convention, though, for convenience of RowExpr
generation and to reduce the risk of breaking extension code.

In HEAD and 9.3, this patch also fixes a problem with some new code in
ruleutils.c that was failing to cope with implicitly-casted joinaliasvars
entries, as per recent report from Feike Steenbergen.  That oversight was
because of an inadequate description of the data structure in parsenodes.h,
which I've now corrected.  There were some pre-existing oversights of the
same ilk elsewhere, which I believe are now all fixed.
Check for NULL result from strdup

Per Coverity Scan
Further hacking on ruleutils' new column-alias-assignment code.

After further thought about implicit coercions appearing in a joinaliasvars
list, I realized that they represent an additional reason why we might need
to reference the join output column directly instead of referencing an
underlying column.  Consider SELECT x FROM t1 LEFT JOIN t2 USING (x) where
t1.x is of type date while t2.x is of type timestamptz.  The merged output
variable is of type timestamptz, but it won't go to null when t2 does,
therefore neither t1.x nor t2.x is a valid substitute reference.

The code in get_variable() actually gets this case right, since it knows
it shouldn't look through a coercion, but we failed to ensure that the
unqualified output column name would be globally unique.  To fix, modify
the code that trawls for a dangerous situation so that it actually scans
through an unnamed join's joinaliasvars list to see if there are any
non-simple-Var entries.
Move strip_implicit_coercions() from optimizer to nodeFuncs.c.

Use of this function has spread into the parser and rewriter, so it seems
like time to pull it out of the optimizer and put it into the more central
nodeFuncs module.  This eliminates the need to #include optimizer/clauses.h
in most of the calling files, demonstrating that this function was indeed a
bit outside the normal code reference patterns.
Fix booltestsel() for case where we have NULL stats but not MCV stats.

In a boolean column that contains mostly nulls, ANALYZE might not find
enough non-null values to populate the most-common-values stats,
but it would still create a pg_statistic entry with stanullfrac set.
The logic in booltestsel() for this situation did the wrong thing for
"col IS NOT TRUE" and "col IS NOT FALSE" tests, forgetting that null
values would satisfy these tests (so that the true selectivity would
be close to one, not close to zero).  Per bug #8274.

Fix by Andrew Gierth, some comment-smithing by me.
pg_upgrade: fix parallel/-j crash on Windows
This fixes the problem of passing the wrong function pointer when doing
parallel copy/link operations on Windows.
Backpatched to 9.3beta.
Found and patch supplied by Andrew Dunstan
pg_upgrade:  more Windows parallel/-j fixes
More fixes to handle Windows thread parameter passing.
Backpatch to 9.3 beta.
Patch originally from Andrew Dunstan
Improve ilist.h's support for deletion of slist elements during iteration.

Previously one had to use slist_delete(), implying an additional scan of
the list, making this infrastructure considerably less efficient than
traditional Lists when deletion of element(s) in a long list is needed.
Modify the slist_foreach_modify() macro to support deleting the current
element in O(1) time, by keeping a "prev" pointer in addition to "cur"
and "next".  Although this makes iteration with this macro a bit slower,
no real harm is done, since in any scenario where you're not going to
delete the current list element you might as well just use slist_foreach
instead.  Improve the comments about when to use each macro.

Back-patch to 9.3 so that we'll have consistent semantics in all branches
that provide ilist.h.  Note this is an ABI break for callers of
slist_foreach_modify().

Andres Freund and Tom Lane
Add GET DIAGNOSTICS ... PG_CONTEXT in PL/PgSQL

This adds the ability to get the call stack as a string from within a
PL/PgSQL function, which can be handy for logging to a table, or to
include in a useful message to an end-user.

Pavel Stehule, reviewed by Rushabh Lathia and rather heavily whacked
around by Stephen Frost.
pg_upgrade: fix initialization of thread argument
Reorder initialization of thread argument marker to it happens before
reap_child() is called.
Backpatch to 9.3.
Improvements to GetErrorContextStack()

As GetErrorContextStack() borrowed setup and tear-down code from other
places, it was less than clear that it must only be called as a
top-level entry point into the error system and can't be called by an
exception handler (unlike the rest of the error system, which is set up
to be reentrant-safe).

Being called from an exception handler is outside the charter of
GetErrorContextStack(), so add a bit more protection against it,
improve the comments addressing why we have to set up an errordata
stack for this function at all, and add a few more regression tests.

Lack of clarity pointed out by Tom Lane; all bugs are mine.
pg_upgrade:  adjust umask() calls
Since pg_upgrade -j on Windows uses threads, calling umask()
before/after opening a file via fopen_priv() is no longer possible, so
set umask() as we enter the thread-creating loop, and reset it on exit.
Also adjust internal fopen_priv() calls to just use fopen().
Backpatch to 9.3beta.
Fix configure probe for sys/ucred.h.

The configure script's test for <sys/ucred.h> did not work on OpenBSD,
because on that platform <sys/param.h> has to be included first.
As a result, socket peer authentication was disabled on that platform.
Problem introduced in commit be4585b1c27ac5dbdd0d61740d18f7ad9a00e268.

Andres Freund, slightly simplified by me.
Don't use SnapshotNow in get_actual_variable_range.

Instead, use the active snapshot.  Per Tom Lane, this function is
most interested in knowing the range of tuples our scan will actually
see.

This is another step towards full removal of SnapshotNow.
pgstattuple: Use SnapshotDirty, not SnapshotNow.

Tuples belonging to uncommitted transactions should not be
counted as dead.

This is arguably a bug fix that should be back-patched, but
as no one ever noticed until it came time to try to get rid
of SnapshotNow, I'm only doing this in master for now.
Change currtid functions to use an MVCC snapshot, not SnapshotNow.

This has a slight performance cost, but the only known consumers
of these functions, known at the SQL level as currtid and currtid2,
is pgsql-odbc; whose usage, we hope, is not sufficiently intensive
to make this a problem.

Per discussion.
pgstattuple: Doc update for previous commit.

In my previous change to make pgstattuple use SnapshotDirty rather
than SnapshotNow, I failed to notice that the documenation also
needed to be updated to match.  Fix.