[tz] Irish Standard Time vs Irish Summer Time

[Zefram]

Stephen Colebourne wrote:
>As I and others have indicated before, this change should not have
>happened. The likelihood of it breaking something was always very
>high, and the alleged reality is that it expresses is a fact that is
>irrelevant to most users (and is disputed anyway). This was change for
>changes sake.

I disagree.  This was change in order to be more accurate: if we're
offering the isdst flag then it ought to reflect what was actually
happening in each jurisdiction.  By its nature this flag is less
objectively defined than the other outputs of the database, but in this
case we have clear evidence that it should be a particular way round.

There was indeed a significant chance of the negative SAVE value breaking
alternate zic implementations, and now that that's turned out to be
the case that's good cause to postpone this correction, or at least the
expressing of it in this natural manner.  The tzdb does have unusually
high stability requirements.  But that's not a reason to keep the database
forever inaccurate.

-zefram