[tz] data not represented in tzfiles

[Zefram]

Paul Eggert wrote:
>There's one remaining zone which has the problem, namely
>Asia/Tehran, but I don't think your 400-year change fixes
>it.

Yeah, that zone doesn't work to a Gregorian-based rule.

>     So, I'm hoping that your fix is no longer needed, in
>that the other two patches have fixed things in a different way.

I don't think that follows.  Even if the 400 year hack is no longer
used for any current zone, that doesn't mean it'll never be applicable
in the future.  If zic is to retain the logic for the 400 year hack,
it ought to be the robustified form of the hack.

-zefram