rem: prfield (int n, struct line *line)
add: prfield (size_t n, struct line const *line)
context: prfield (int n, struct line *line){  size_t len;  if (n < line->nfields)    {      len = line->fields[n].len;      if (len)	fwrite (line->fields[n].beg, 1, len, stdout);      else if (empty_filler)	fputs (empty_filler, stdout);    }  else if (empty_filler)    fputs (empty_filler, stdout);}