addHeader :: ByteString -> Response -> Response
addHeader org (ResponseFile    s headers fp m) = 
               ResponseFile    s (modified headers org) fp m
addHeader :: ByteString -> Response -> Response
addHeader org (ResponseFile    s headers fp m) = 
               ResponseFile    s (modified headers org) fp m
addHeader org (ResponseFile    s headers fp m) = 
               ResponseFile    s (modified headers org) fp m