OAK-1163: Observation events should respect permissions
First draft for AC filtering of observation events

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1543881 13f79535-47bb-0310-9956-ffa450edef68
minor improvement: make ImmutableTree#state private and add #unwrap() method -> used by ImmutableRoot

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1543883 13f79535-47bb-0310-9956-ffa450edef68