# File lib/ftw/http/headers.rb, line 50
  def add(field, value)
    field = field.downcase
    if @headers.include?(field)
      if @headers[field].is_a?(Array)
        @headers[field] << value
      else
        @headers[field] = [@headers[field], value]
      end
    else
      set(field, value)
    end
  end