OAK-1446: Offline tool to repair TarMK

Improved debug output

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1586363 13f79535-47bb-0310-9956-ffa450edef68
OAK-1696: Repository fails to restart on Windows

Avoid memory-mapping a tar file before we're sure that it has a valid index.
Make the recovery code in TarReader more resilient against unexpected problems.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1586364 13f79535-47bb-0310-9956-ffa450edef68