[tz] [PATCH] New file 'pre1970' for zones that differ only in pre-1970 time stamps.

[Zefram]

Paul Eggert wrote:
>For example, tzwinnow -a 1970z should find that
>Africa/Accra and Africa/Dakar are duplicates, since
>they've both been at plain GMT since 1970, but tzwinnow
>considers them to be distinct for some reason.

Good catch.  The logic around the transition to the POSIX-TZ rule
is wonky.  It's perceiving the zones as different because their last
transitions are at different times, even though that's 1942-12-30 vs
1941-06-01.  I'll fix that.

>One suggestion: it would be nice for tzwinnow to have
>an option where it ignores differences due only to the
>time zone abbreviations, for applications that care only
>about UTC offsets.

Sure.  It also compares the is_dst flag; I can make that all optional.

I'd noticed that the Russian timezones don't merge when tzselect applies
winnowing.  This is partly due to using different initialisms even when
the base offset is shared.

-zefram