bug#641: format-time-string %Z does not work, starting with Emacs 22.2

[Eli Zaretskii]

> From: "Drew Adams" <drew.adams@oracle.com>
> Date: Fri, 8 Aug 2008 08:57:11 -0700
> Cc: 
> 
> IOW, we should give users _both_ possibilities unambiguously: Posix-only and
> possibly-non-Posix, better-than-nothing, YMMV, human-readable name.
> 
> We can do that by introducing a new format key, in addition to %Z.

I'm okay with having a new format, or with adding a function that
would return a time-zone name that is just a string, not the spec
codified by Posix.  (It could return strings like "Asia/Riyadh" on
Posix platforms.)