def csv_to_s(rows, cols: nil)
      string = ""
      f = CSV.new(StringIO.new(string))
      csv_write0(f, rows, cols: cols)
      string
    end
def csv_to_s(rows, cols: nil)
      string = ""
      f = CSV.new(StringIO.new(string))
      csv_write0(f, rows, cols: cols)
      string
    end
Returns a string containing +rows+ as a csv. Similar to csv_write.