Timeout when using authenticated proxy for https request

I get a timeout when I run this

```
import requests

proxies = {
    'https': 'https://username:password@ip:port',
}
resp = requests.get('https://www.google.com/', proxies=proxies)
print resp.status_code`
```

This worked in 0.7.6, then 0.8.0 - 0.8.5 there's the `ValueError: invalid literal for int() with base 10: 'user:pass@ip:port'` that contains the proxy details. Then 0.8.6/7 it just takes ages then times out. Here's the stacktrace if I kill it manually

```
^CTraceback (most recent call last):
  File "test.py", line 6, in <module>
    resp = requests.get('https://www.google.com/', proxies=proxies)
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/api.py", line 79, in get
    return request('get', url, **kwargs)
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/api.py", line 66, in request
    prefetch=prefetch
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/sessions.py", line 191, in request
    r.send(prefetch=prefetch)
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/models.py", line 462, in send
    timeout=self.timeout,
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/packages/urllib3/poolmanager.py", line 123, in urlopen
    return self.proxy_pool.urlopen(method, url, **kw)
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/packages/urllib3/connectionpool.py", line 334, in urlopen
    body=body, headers=headers)
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/packages/urllib3/connectionpool.py", line 215, in _make_request
    conn.request(method, url, **httplib_request_kw)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 941, in request
    self._send_request(method, url, body, headers)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 975, in _send_request
    self.endheaders(body)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 937, in endheaders
    self._send_output(message_body)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 797, in _send_output
    self.send(msg)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 759, in send
    self.connect()
  File "/Users/peter/.virtualenvs/my_project/lib/python2.7/site-packages/requests/packages/urllib3/connectionpool.py", line 72, in connect
    ca_certs=self.ca_certs)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ssl.py", line 344, in wrap_socket
    ciphers=ciphers)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ssl.py", line 121, in __init__
    self.do_handshake()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ssl.py", line 283, in do_handshake
    self._sslobj.do_handshake()
KeyboardInterrupt
```

Here's where the error happens https://github.com/kennethreitz/requests/blob/develop/requests/models.py#L469 but I'm not sure of the cause. I'm pretty sure this is related to #293.