On the log-addressing branch:  Finalize the pack concurrency work.
All read code should now work fine in parallel to a background pack run.

This patch makes lets the index verification code retry a shard when
it got packed while being verified.

* subversion/libsvn_fs_fs/verify.c
  (verify_index_consistency): retry upon error if the pack size changed


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-addressing@1532084 13f79535-47bb-0310-9956-ffa450edef68