TooManyRedirects not working in 2.4.0

[ondrejsika]

hi,

if i try page which has permanent redirect to it self, requests (2.4.0) cant raise TooManyRedirects exception. In 2.3.0 works fine.

try:

import requests
requests.get('http://www.dx.com/p/-268479')

[Lukasa]

Hurrah! As I predicted in #2095, our redirect cache has introduced a bug.

Specifically, if a website sets a permanent redirect to itself we will spin in an infinite loop forever on line 535 of sessions.py, trying to find the "real" url.

My proposed fix would be to change the logic where we add to the redirect cache (L138 of sessions.py) from this:

if resp.is_permanent_redirect:
    self.redirect_cache[req.url] = prepared_request.url

to this:

# Cache the URL unless it's a redirect to self.
if resp._is_permanent_redirect and req.url != prepared_request.url:
    self.redirect_cache[req.url] = prepared_request.url

[sigmavirus24]

Don't be too happy @Lukasa. =P