OAK-1300 Removing a reference from a mv property destroys the reverse lookup from the remaining

also fixes:
- OAK-1299 Removing user from group also invalidates other members memberships

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1552460 13f79535-47bb-0310-9956-ffa450edef68