libical: revert r1130 (VTIMEZONE transitions)

[Patrick Ohly]

On Sun, 2015-06-07 at 11:11 -0400, Allen Winter wrote:
> Howdy,
> 
> I intend to revert the old commit 1130 from 3 years ago for the upcoming 2.0 release.
> Commit message:
> "Fix TZ rules, make the VTIMEZONE specifier an exact mirror of the transitions in the
> zone files, so it now uses absolute dates rather than trying to calculate a RRULE.
> Patch frmo jejb, THanks!
> Fixes bug IDs: 3432224, 3405041, 2096602
> also the timezone test program passes 100% now."
> 
> It caused several problems pointed out by Patrick, see https://sourceforge.net/p/freeassociation/bugs/95/

I can add that it has also exaggerated performance issues in Radicale
where that CalDAV server included all defined VTIMEZONEs in each
individual item (= one VEVENT), regardless of which time zones were used
in the item.

> reverting might bring back  https://sourceforge.net/p/freeassociation/bugs/34/ but that bug was from Patrick too

Re-reading that bug it seems to me that the Evolution fork must have had
some bug fixes which did not find their way into upstream libical. But
it's very hard to be sure anymore.

> If anyone objects to this plan please let me know asap.

I'm in favor of it.

But it would be good to hear also from those who originally proposed
commit 1130. The commit message mentions bug numbers, but I don't know
in which bug tracker.

Ultimately the key problem remains: some users of libical need exact
VTIMEZONEs, others need interoperable ones. libical cannot provide both
at the same time, so someone needs to choose, either at compile time or
runtime.

Best Regards, Patrick Ohly