[ Sorry for not having one diff which creates new files, but "cvs diff -N"
  seems to be ignoring that little 'N' ]

The attached patch and files, which includes documentation, adds a new
loadable module, zsh/regex.  I've not examined widechar issues and which
regex libraries actually do handle these.  I've not looked at linkage
issues on platforms where regex (the POSIX interface, not regexp) is not
a part of libc.

This also includes my previous =~ work, replacing the previous patch.
I'm not sure that auto-unsetting REMATCH_PCRE is a good idea, so invite
comments; also as to which should be the default value; I suppose that
if pcre is not the default, then the warning can be put back in ...

My only test platform has been freebsd/amd64.

I've also cleaned up various memory leaks in zsh/pcre.
zsh/pcre now also sets $MATCH, not just $match.

I went with having $BASH_REMATCH be set instead of, rather than in
addition to, $MATCH and $match.  I'm again very open to persuasion here.

Oh, and the copyright notice in regex.c seems a bit disjointed, with
multiple names.  What's the copyright policy on newly contributed files?

zsh/regex provides the -regex-match conditional operator, the knowledge
of -regex-match and -pcre-match remains in cond.c with the COND_REGEX
handling for =~.

Also, I've decided that I much prefer the PCRE API to the POSIX regex
API.  :-)  I'm off to drink more wine to recover.

-Phil