Journaler: warn and shut down if we hit end of journal too early
If a gap gets created in the journal, the Journaler shuts down replay but doesn't warn that it hit ENOENT unexpectedly early (or didn't find a LogEvent, or whatever). Often this happens at a point when the Journaler knows that there should be data available. In that case, the Journaler should print a warning and shut down the MDS (with an option to not do so, of course). This could prevent a lost journal object from eradicating all updates in the following objects.