Cookie method can not set more than one cookie per request

[Nane Kratzke]

Cookie method of Response is not able to set more than one cookie per response.

I think header method is buggy.

  header(String name, [value]) {
    if (value == null) {
      return _response.headers[name];
    }
    _response.headers.set(name, value);
    return this;
  }

should be:

  header(String name, [value]) {
    if (value == null) {
      return _response.headers[name];
    }
    _response.headers.__add__(name, value);
    return this;
  }

[Yehor Lvivski]

Fixed, thanks!