ability to specify minModificationTimeMillis as arg

as an argument to JobFilePreProcessor. Only files after this timestamp will be picked up. Still honor lastProcessRecord.
Do we need any more tight checks on this?
Do we allow extremely small dates (like earlier than the Hadoop project existed) or some date in the future ?
Those would probably indicate a mis-understanding of the argument and likely be an error.
How about negative numbers, those would clearly not be a valid date, but would pass for < or = comparisons silently in perhaps unexpected ways.