fix the redirections with SetCookie, if the domain is consistent.

[ptrsxu]

if we access http://www.httpbin.org/cookies/set?k2=v2&k1=v1 with the GET method, the server would return a 302 FOUND with

Location:/cookies
Server:gunicorn/19.7.1
Set-Cookie:k1=v1; Path=/
Set-Cookie:k2=v2; Path=/

in response header, the next request should have the cookie k1=v1 and k2=v2 with it if the redirected location has the same domain with the referer, and finally we can get a content with:

{
  "cookies": {
    "k1": "v1", 
    "k2": "v2"
  }
}

This pull request will fix the problem.

[seanmonstar]

This should mean that the sent Cookie headers will contain all the attributes from the Set-Cookie header, aka we'd be sending Cookie: foo=bar; Path=/; Domain=foo.bar; Expires=123, when it should just be Cookie: foo=bar.

Additionally, we could be sending cookies incorrectly. The Path and Domain of the set cookie could possibly not match the new location.

All this logic is tricky to get correct, but it is a goal of reqwest to do it. See #14.

[ptrsxu]

I check it again and the idea is indead half-baked , I would go deeper into it.