am 23b83547: only add new attendees, delete removed attendees on event edits.

Merge commit '23b83547cc5d60a173b61c2dc2e627ce7c14f665' into eclair-plus-aosp

* commit '23b83547cc5d60a173b61c2dc2e627ce7c14f665':
  only add new attendees, delete removed attendees on event edits.