Fix misplaced right paren bugs in pgstatfuncs.c.

The bug would only show up if the C sockaddr structure contained
zero in the first byte for a valid address; otherwise it would
fail to fail, which is probably why it went unnoticed for so long.

Patch submitted by Joel Jacobson after seeing an article by Andrey
Karpov in which he reports finding this through static code
analysis using PVS-Studio.  While I was at it I moved a definition
of a local variable referenced in the buggy code to a more local
context.

Backpatch to all supported branches.
Properly detect invalid JSON numbers when generating JSON.

Instead of looking for characters that aren't valid in JSON numbers, we
simply pass the output string through the JSON number parser, and if it
fails the string is quoted. This means among other things that money and
domains over money will be quoted correctly and generate valid JSON.

Fixes bug #8676 reported by Anderson Cristian da Silva.

Backpatched to 9.2 where JSON generation was introduced.
Don't attempt to limit target database for pg_restore.

There was an apparent attempt to limit the target database for
pg_restore to version 7.1.0 or later.  Due to a leading zero this
was interpreted as an octal number, which allowed targets with
version numbers down to 2.87.36.  The lowest actual release above
that was 6.0.0, so that was effectively the limit.

Since the success of the restore attempt will depend primarily on
on what statements were generated by the dump run, we don't want
pg_restore trying to guess whether a given target should be allowed
based on version number.  Allow a connection to any version.  Since
it is very unlikely that anyone would be using a recent version of
pg_restore to restore to a pre-6.0 database, this has little to no
practical impact, but it makes the code less confusing to read.

Issue reported and initial patch suggestion from Joel Jacobson
based on an article by Andrey Karpov reporting on issues found by
PVS-Studio static code analyzer.  Final patch based on analysis by
Tom Lane.  Back-patch to all supported branches.