def []= k, v   
      split_fields if not @h
      kupper = k.upcase
      @h[kupper] = v
      @original_key[kupper] = k
    end
def []= k, v   
      split_fields if not @h
      kupper = k.upcase
      @h[kupper] = v
      @original_key[kupper] = k
    end
Set INFO fields (used by --rewrite)