Add a 1 ms MAX_OFFSET of new_time compared to newest_time_stamp

* this allows for the newest_time_stamp to precurse the reported
  Wall clock time by 1 ms. This should be enough, since it can
  accomodate 500_000 new facts entered (in that 1 ms) and by then
  the reported Wall time will have advanced by at least 1 ms.
* is mainly an issue on JRuby (because of the 1 ms granularity
  in the Wall Clock).