Wrap multixact/members correctly during extension, take 2

In a50d97625497b7 I already changed this, but got it wrong for the case
where the number of members is larger than the number of entries that
fit in the last page of the last segment.

As reported by Serge Negodyuck in a followup to bug #8673.
Fix infinite loop when splitting inner tuples in SPGiST text indexes.

Previously, the code used a node label of zero both for strings that
contain no bytes beyond the inner tuple's prefix, and for cases where an
"allTheSame" inner tuple has to be split to allow a string with a different
next byte to be inserted into it.  Failing to distinguish these cases meant
that if a string ending with the current prefix needed to be inserted into
an allTheSame tuple, we got into an infinite loop, because after splitting
the tuple we'd descend into the child allTheSame tuple and then find we
need to split again.

To fix, instead use -1 and -2 as the node labels for these two cases.
This requires widening the node label type from "char" to int2, but
fortunately SPGiST stores all pass-by-value node label types in their
Datum representation, which means that this change is transparently upward
compatible so far as the on-disk representation goes.  We continue to
recognize zero as a dummy node label for reading purposes, but will not
attempt to push new index entries down into such a label, so that the loop
won't occur even when dealing with an existing index.

Per report from Teodor Sigaev.  Back-patch to 9.2 where the faulty
code was introduced.
Forward-port regression test for bug #10587 into 9.3 and HEAD.

Although this bug is already fixed in post-9.2 branches, the case
triggering it is quite different from what was under consideration
at the time.  It seems worth memorializing this example in HEAD
just to make sure it doesn't get broken again in future.

Extracted from commit 187ae17300776f48b2bd9d0737923b1bf70f606e.
Stamp HEAD as 9.5devel.

Let the hacking begin ...
Stamp shared-library minor version numbers for 9.5.
Fix ancient encoding error in hungarian.stop.

When we grabbed this file off the Snowball project's website, we mistakenly
supposed that it was in LATIN1 encoding, but evidently it was actually in
LATIN2.  This resulted in ő (o-double-acute, U+0151, which is code 0xF5 in
LATIN2) being misconverted into õ (o-tilde, U+00F5), as complained of in
bug #10589 from Zoltán Sörös.  We'd have messed up u-double-acute too,
but there aren't any of those in the file.  Other characters used in the
file have the same codes in LATIN1 and LATIN2, which no doubt helped hide
the problem for so long.

The error is not only ours: the Snowball project also was confused about
which encoding is required for Hungarian.  But dealing with that will
require source-code changes that I'm not at all sure we'll wish to
back-patch.  Fixing the stopword file seems reasonably safe to back-patch
however.
Fix typos in comments.