rewind added to DataClone to fix bug of different length of data

[raptoravis]

rewind is called in _runnext, it needs to be matched with advance

              # make sure only those at dmaster level end up delivering
                for i, dti in enumerate(dts):
                    if dti is not None:
                        di = datas[i]
                        rpi = False and di.replaying   # to check behavior
                        if dti > dt0:
                            if not rpi:  # must see all ticks ...
                                di.rewind()  # cannot deliver yet
                            # self._plotfillers[i].append(slen)
                        elif not di.replaying:
                            # Replay forces tick fill, else force here
                            di._tick_fill(force=True)

                        # self._plotfillers2[i].append(slen)  # mark as fill