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

[Drew Adams]

> From: martin rudalics Sent: Monday, August 04, 2008 2:24 PM
>  > emacs -Q
>  > M-: (format-time-string "%Z) ==> ""
>  > M-: (format-time-string "%z) ==> "-0700"
>  >
>  > The %Z string is incorrect. In my case, it should be (as it is in
>  > Emacs 20 and Emacs 22.1): "Pacific Daylight Time".
>  >
>  > This same bug appears in Emacs 23.  This is a regression from Emacs
>  > 22.1.
> 
> See
> 2007-06-07  Jason Rumney  <jasonr@gnu.org>
>       * s/ms-w32.h: Don't define HAVE_TZNAME.
>       * editfns.c (Fcurrent_time_zone): Remove hack for 
>       Japanese Windows.
> 
> and the preceding discussion starting with
> http://lists.gnu.org/archive/html/emacs-devel/2007-06/msg00334.html

Sorry; I don't know what all of that means.

It is obviously a bug, however, that %Z produces an empty time-zone string. I
use it for a time stamp, for instance, with this form:
 (format-time-string "%a %b %e %T %Y (%Z)")

After the change that introduced the bug, I get this:

Mon Aug  4 15:01:16 2008 ()

instead of this:

Mon Aug  4 15:01:16 2008 (Pacific Daylight Time)

The doc string for `format-time-string' says that "%Z is the time zone name". My
time zone name is "Pacific Daylight Time" (or something similar). It is
certainly not "".