OAK-2074: _lastRev recovery tool

First implementation of the recovery tool. It supports a dryRun mode, which only checks the repository and logs the result. Without this option, the tool will apply the required changes.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1622428 13f79535-47bb-0310-9956-ffa450edef68