def get_fields(key)
    return nil unless @header[key.downcase]
    @header[key.downcase].dup
  end
[Ruby 1.8.3]
Returns an array of header field strings corresponding to the
case-insensitive +key+.  This method allows you to get duplicated
header fields without any processing.  See also #[].

p response.get_fields('Set-Cookie')
#=> ["session=al98axx; expires=Fri, 31-Dec-1999 23:58:23",
"query=rubyscript; expires=Fri, 31-Dec-1999 23:58:23"]
p response['Set-Cookie']
#=> "session=al98axx; expires=Fri, 31-Dec-1999 23:58:23, query=rubyscript; expires=Fri, 31-Dec-1999 23:58:23"