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

["Drew Adams" <drew.adams@oracle.com>]

> We could at least provide this, and if the mapping fails we 
> could print a message that it's an unknown string, and the
> user can submit a bug. %Z could show the full Windows-provided
> name, which IMHO is better than nothing.

Yes, my point from the beginning is that the Windows name can be better than
nothing, depending on your needs.

It depends on what you want/need in any given context. I agree with Eli that we
also need to let users specify, when they need it, a name guaranteed to be
Posix-compliant, which would be "" if no other Posix name is appropriate.

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. Either %Z or
the new key can be for the better-than-nothing, human-readable name. %Z for this
has the advantage of backward compatibility. %Z for the Posix-compliant name has
the advantage that "Z" is itself a Posix convention.

I'm OK with either approach. The important thing is to give users the option of
specifying either name format, depending on their needs.