code: @Override
    public List<TimelineObjectHolder<VersionType, ObjectType>> lookup(Interval interval)
    {
      try {
        lock.readLock().lock();
        return lookup(interval, false);
      }
      finally {
        lock.readLock().unlock();
      }
    }
docs: Does a lookup for the objects representing the given time interval.  Will *only* return
  PartitionHolders that are complete.
  
  @param interval interval to find objects for
  
  @return Holders representing the interval that the objects exist for, PartitionHolders
  are guaranteed to be complete