1.0.37.36: revisit FIND/POSITION bounds checking on lists

  The spec doesn't actually /require/ us to signal an error if we
  are not in danger of running out of bounds as far as I can tell.

  So don't traverse the entire list during forward searches if we
  find what we are looking for before specified :END or the list end.

  Patch by Alec Berryman.

  This revisits lp#452008, and fixed lp#554385.