This corresponds to the upstream MR.

@blam, this is a rewrite of your patch fixing the issue in deleteIncidenceInstances(). Looking closer to the deleteIncidence() function it is calling, I've noticed that this delete function is misbehaving for occurrences because it is not paying attention to the recurrenceId... I've taken the liberty to rewrite your patch, because both issues while being distinct are related together. I hope you don't mind. I've added a test also for upstream. Let see what they say upstream about this. I'll rework the patch here after it will be accepted with or without revisions.

@chriadam, for your information, some hickups of the transition...