allow_redirects=True for one get affects the next one

Here is an example with 3 similar `get` calls with all allow_redirects=False:

```
$> PYTHONPATH=$PWD python -c "import requests; url = 'http://127.0.0.1:45508/ds666'; sess = requests.Session(); print sess.get(url, allow_redirects=False); print sess.get(url, allow_redirects=False); print sess.get(url, allow_redirects=False)"                                                                  
<Response [301]>
<Response [301]>
<Response [301]>
```

all of them logically 301.  If 2nd one says to allow redirects, then 3rd would also succeed even if I disallow redirects for that invocation

```
$> PYTHONPATH=$PWD python -c "import requests; url = 'http://127.0.0.1:45508/ds666'; sess = requests.Session(); print sess.get(url, allow_redirects=False); print sess.get(url, allow_redirects=True); print sess.get(url, allow_redirects=False)"
<Response [301]>
<Response [200]>
<Response [200]>
```

Demonstrated on

```
v2.9.1-63-g6143b7e
```


Good spot! I suspect this might be the result of the 301 cache misbehaving somewhat. @sigmavirus24, does that sound right to you?


Yikes, this is a nasty bug.


I actually can't reproduce this, using the code available in our `master` branch.


copy paste after me! ;)

```
hopa:/tmp
$> git clone  https://github.com/kennethreitz/requests
Cloning into 'requests'...
remote: Counting objects: 16549, done.
remote: Compressing objects: 100% (18/18), done.
remote: Total 16549 (delta 7), reused 0 (delta 0), pack-reused 16530
Receiving objects: 100% (16549/16549), 6.78 MiB | 10.12 MiB/s, done.
Resolving deltas: 100% (9464/9464), done.
Checking connectivity... done.
2 31038.....................................:Fri 05 Feb 2016 04:00:55 PM EST:.
hopa:/tmp

$> cd requests 
AUTHORS.rst      HISTORY.rst  MANIFEST.in  NOTICE      docs/  requests/         setup.cfg  tests/
CONTRIBUTING.md  LICENSE      Makefile     README.rst  ext/   requirements.txt  setup.py*
2 31039.....................................:Fri 05 Feb 2016 04:00:57 PM EST:.
(git)hopa:/tmp/requests[master]

$> git describe
v2.6.2-327-gbbadf47
2 31040.....................................:Fri 05 Feb 2016 04:01:03 PM EST:.
(git)hopa:/tmp/requests[master]

$> PYTHONPATH=$PWD python -c "import requests; print requests.__version__"                        
2.9.1              
2 31041.....................................:Fri 05 Feb 2016 04:01:14 PM EST:.
(git)hopa:/tmp/requests[master]

$> git describe --tags                                                    
v2.9.1-65-gbbadf47
2 31042.....................................:Fri 05 Feb 2016 04:01:17 PM EST:.
(git)hopa:/tmp/requests[master]git

$> PYTHONPATH=$PWD python -c "import requests; print requests.__version__"
2 31042 ->1.....................................:Fri 05 Feb 2016 04:01:22 PM EST:.
(git)hopa:/tmp/requests[master]git

$> python -m SimpleHTTPServer &                                                                   
[1] 25321                      
2 31043 [1].....................................:Fri 05 Feb 2016 04:01:26 PM EST:.
(git)hopa:/tmp/requests[master]git

$> Serving HTTP on 0.0.0.0 port 8000 ...

2 31043 [1].....................................:Fri 05 Feb 2016 04:01:28 PM EST:.
(git)hopa:/tmp/requests[master]git

$> PYTHONPATH=$PWD python -c "import requests; url = 'http://127.0.0.1:8000/docs'; sess = requests.Session(); print sess.get(url, allow_redirects=False); print sess.get(url, allow_redirects=True); print sess.get(url, allow_redirects=False)"     
127.0.0.1 - - [05/Feb/2016 16:01:56] "GET /docs HTTP/1.1" 301 -
<Response [301]>
127.0.0.1 - - [05/Feb/2016 16:01:56] "GET /docs HTTP/1.1" 301 -
127.0.0.1 - - [05/Feb/2016 16:01:56] "GET /docs/ HTTP/1.1" 200 -
<Response [200]>
127.0.0.1 - - [05/Feb/2016 16:01:56] "GET /docs/ HTTP/1.1" 200 -
<Response [200]>
```


Ah, it looks like this is occuring with 301 redirects, not 302s.


@yarikoptic thanks for the help, this should now be fixed.


cool.  Thanks!