Do not trigger dirty fields with no changes
Only executing a set function should not automatically add fields to
isDirty, where there were no changes.
Do not increment revision, if only a schedulingid is added
Search for existing incidences also by instanceIdentifier
When we have also to use other clients, that update the calendar we have
to make sure, that kontact is RFC conform. Other clients, do not use
scheduling Id, so we have to make sure, we find the incidences by
uid+recurrence id.
Make sure, that cancel mails are sent, if event is deleted
This change was done to fix the itiphelper tests.