OAK-571 - Limit usage of headRevId in sync collection to non-branches 

Now headRevId in sync collection is only updated for trunk commits. Also updated the mongo java driver version.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1437278 13f79535-47bb-0310-9956-ffa450edef68