Also set the detached-and-synced flag when updating an exception
Updating an exception was missing the detached-and-synced flag, making this event marked as local modification at next delta calculation. Add a test to demonstrate the bug.
Also remove the comment with the flag when upstreaming.
Note that this change modify slightly updateIncidence(). Now, passing empty uri or etag make them removed and not update them with empty values. This should not affect behaviour since in plugin this routine is always called with non-empty strings. But one test has to be updated.