OAK-672: Avoid JCR APIs calling other JCR APIs
- Clean up ImportHandler and SessionImporter

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1456030 13f79535-47bb-0310-9956-ffa450edef68
OAK-619 Lock-free MongoMK implementation
- need to make more methods synchronized otherwise it may happen getHeadRevision() sees intermediate state of a commit() call

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1456031 13f79535-47bb-0310-9956-ffa450edef68