I now sorted out the changes that we did on kcalcore:

• added support to not change the dirtyfileds if the value hasn't changed
• support for the same event in different calendars:
  • If one event is part of mutiple calendars korganzier must know this to handle this, this happens if you look at other persons calendars and they are also attendee in the same event. We need a way to define exact the event in one akonadi calendar and not randomly return one with the correct uid.
• add postCalendarIncidenceDeleted signal to act before and after a incidence is deleted.