Centralize libpq's low-level code for dropping a connection.

Create an internal function pqDropConnection that does the physical socket
close and cleans up closely-associated state.  This removes a bunch of ad
hoc, not always consistent closure code.  The ulterior motive is to have a
single place to wait for a spawned child backend to exit, but this seems
like good cleanup even if that never happens.

I went back and forth on whether to include "conn->status = CONNECTION_BAD"
in pqDropConnection's actions, but for the moment decided not to.  Only a
minority of the call sites actually want that, and in any case it's
arguable that conn->status is slightly higher-level state, and thus not
part of this function's purview.
Adjust PL/Python regression tests some more for Python 3.3.

Commit 2cfb1c6f77734db81b6e74bcae630f93b94f69be fixed some issues caused
by Python 3.3 choosing to iterate through dict entries in a different order
than before.  But here's another one: the test cases adjusted here made two
bad entries in a dict and expected the one complained of would always be
the same.

Possibly this should be back-patched further than 9.2, but there seems
little point unless the earlier fix is too.
Use .NOTPARALLEL in ecpg/Makefile to avoid a gmake parallelism bug.

Investigation shows that some intermittent build failures in ecpg are the
result of a gmake bug that was reported quite some time ago:
http://savannah.gnu.org/bugs/?30653

Preventing parallel builds of the ecpg subdirectories seems to dodge the
bug.  Per yesterday's pgsql-hackers discussion, there are some other things
in the subdirectory makefiles that seem rather unsafe for parallel builds
too, but there's little point in fixing them as long as we have to work
around a make bug.

Back-patch to 9.1; parallel builds weren't very well supported before
that anyway.
Make plperl safe against functions that are redefined while running.

validate_plperl_function() supposed that it could free an old
plperl_proc_desc struct immediately upon detecting that it was stale.
However, if a plperl function is called recursively, this could result
in deleting the struct out from under an outer invocation, leading to
misbehavior or crashes.  Add a simple reference-count mechanism to
ensure that such structs are freed only when the last reference goes
away.

Per investigation of bug #7516 from Marko Tiikkaja.  I am not certain
that this error explains his report, because he says he didn't have
any recursive calls --- but it's hard to see how else it could have
crashed right there.  In any case, this definitely fixes some problems
in the area.

Back-patch to all active branches.
Add vcregress.pl target for checking pg_upgrade.

This follows recent addition of Windows/Mingw testing.
Backpatch to Release 9.2 so we can get some buildfarm testing
going.
Fix typo: lexemes misspelled in full text search docs.

Dan Scott
Fix logical errors in tsquery selectivity estimation for prefix queries.

I made multiple errors in commit 97532f7c29468010b87e40a04f8daa3eb097f654,
stemming mostly from failure to think about the available frequency data
as being element frequencies not value frequencies (so that occurrences of
different elements are not mutually exclusive).  This led to sillinesses
such as estimating that "word" would match more rows than "word:*".

The choice to clamp to a minimum estimate of DEFAULT_TS_MATCH_SEL also
seems pretty ill-considered in hindsight, as it would frequently result in
an estimate much larger than the available data suggests.  We do need some
sort of clamp, since a pattern not matching any of the MCELEMs probably
still needs a selectivity estimate of more than zero.  I chose instead to
clamp to at least what a non-MCELEM word would be estimated as, preserving
the property that "word:*" doesn't get an estimate less than plain "word",
whether or not the word appears in MCELEM.

Per investigation of a gripe from Bill Martin, though I suspect that his
example case actually isn't even reaching the erroneous code.

Back-patch to 9.1 where this code was introduced.