[dev] iCalendar stuff

[Karsten Fourmont]

> [ 4) ignore "UID:" in api import/replace or not ]
> 
>>We can't completely ignore them - that'd break iCalendar updates. We
>>need to not
>>use external UIDs as the primary key, but we *do* need to maintain a
>>map of the original external UID.

OK, finally I understand what you meant :-)
But how it?

I've got 3 ideas, none seem to completly solve the problem:

1) add new "uid" field to table kronolith_events
2) store uid in datatree
3) try to use external UID as primary key if possible. If not, to some 
clever fallback to what?? 2)??

Drawbacks:

1) works only with our mysql backend. Not good.
2) may work, but I don't like an "use DataTree for everything" approach. 
If you browse the horde logs on debug level, you alreay see way too many 
datatree queries
3) I don't know. Using external data as primary key just doesn't seem 
right...

We might end up with 2)

Any ideas anyone?

  Karsten