[tz] draft of change summary for next tz release

[Alan Barrett]

On Tue, 17 Sep 2013, Stephen Colebourne wrote:
>On 17 September 2013 22:38, Paul Eggert <eggert at cs.ucla.edu> wrote:
>>   Changes affecting time stamps before 1970
>>
>>     Some zones have been turned into links, when they differ from
>>     existing zones only in older data that was likely invented or that
>>     differs only in LMT or transition from LMT.  These changes affect
>>     only time stamps before 1943.  The affected zones are:
>>     Africa/Juba, America/Anguilla, America/Aruba, America/Dominica,
>>     America/Grenada, America/Guadeloupe, America/Marigot,
>>     America/Montserrat, America/St_Barthelemy, America/St_Kitts,
>>     America/St_Lucia, America/St_Thomas, America/St_Vincent,
>>     America/Tortola, and Europe/Vaduz.
>
> From my perspective, these are the only changes that concern me.

I also disagree with this change, except when two zones differ 
only in LMT value, in which case I think it's fine to convert one 
to a link.

If two zones differ in date of transition form LMT to standard 
time, then I think that we should retain that information, not 
convert one to a link, even if the difference is only in pre-1970 
data.

If we know that old data was wrong, then we should correct it, 
but if we merely suspect that the old data is unreliable then we 
should retain our best estimate, not remove it.

--apb (Alan Barrett)