OAK-593: Segment-based MK

Use soft references in OffsetCache to avoid wasting memory on unused bits

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1450714 13f79535-47bb-0310-9956-ffa450edef68
OAK-51 : Access Control Management (unused import)

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1450716 13f79535-47bb-0310-9956-ffa450edef68