HEADS-UP: /bin/sh memory management bug fixes committed

[Robert Elz <kre%munnari.OZ.AU@localhost>]

I have just committed the (long awaited) bug fix set for /bin/sh --
to fix some bugs I introduced recently - but also, several old,
devious, bugs that had remained hidden for years, but which became
more exposed with some of the recent changes - not so much the changes
themselves, but with the way the code changed to accommodate easier
debugging of the changes.

So please watch for anything that looks like it could be shell misbehaviour,
and either let me know, or file a PR.

You might also want to consider rebuilding anything that has been built from
a shell script (particularly a large one - like a configure script) in the
past couple of weeks.   While it is very unlikely that a bug could have
caused the script to fail in a way that would not be immediately obvious,
with some of what has been fixed, almost anything is possible.  Note it is
not so much the complexity of the script that matters, but the amount of
data processed (strings expanded, ...) which would trigger problems, so a
small script that collects, massages, then outputs, a lot of variable
length (but probably normally lengthy) data is far more likely to have been
affected than a huge set of functions that work on a relatively small data set.

While doing this, a couple of user visible changes just "snuck in"
while I wasn't looking...

Posix requires that '~' expand to he value of $HOME when HOME is set.
We were doing that, except in the case where HOME="" where we left the ~
in place instead of replacing it with the null string as required (the
same was true for the even less likely case of ~user being found in the
passwd file and having an empty home directory set there - we should be
returning a null string in that case as well, and weren't, but now do.)

If HOME is unset, then it is unspecified in POSIX what happens - we used
to simply leave the ~, now I have made the shell return
	 getpwuid(getuid())->pw_home
(assuming that exists of course).   This allows a script to compensate for
being run with "env -i" (or similar) if it desires, which was more difficult
before.   While many other shells retain our past behaviour (just leaving
the '~') when HOME is unset, others do it the new way (this difference is
why POSIX does not specify what must happen.)

If anyone finds that this change causes problems, let me know, this was
a trivial change, and would be easy to revert.

There is also one additional fix to an obscure case of counting LINENO with
"here documents" when a bizarre (and not working in many shells) end delimiter
(containing newline characters) is used.   Never seen it in real life, so I
doubt anyone will notice the difference (and this one was a bug fix.)

kre