anchor.diff:  
   !--- In-place quicksort.  Uses the sample code in Numerical Recipies as a base.  ---
   
  -    pure subroutine qsort_i0_list(list, head, nsort)
  +    pure subroutine qsort_i0_list(list, head, nsort, tail)
   
           ! Sort a 2D array of i0 integers.
   
  
positive.code:         ! In/Out:
          !    list: 2D array of i0 integers.  Sorted on output.
          ! In:
          !    head (optional): sort list up to and including list(:,:head) and
          !        leave the rest of the array untouched.  Default: sort the
          !        entire array.
  
negative.code:         end if
  
          nstack = 0
  
          if (present(tail)) then
              lo = tail
          else
              lo = 1
          end if
          if (present(head)) then
              hi = head
          else
  