fix proxy url

This fixes the proxy URL for the requests library (python-requests-1.1.0). You will need the protocol in the url otherwise you will receive a Invalid Argument exception.

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~ $ python
Python 2.6.6 (r266:84292, May 27 2013, 05:35:12) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import requests
>>> r = requests.get("http://yum.mariadb.org/5.5/rhel6-amd64/repodata/repomd.xml", proxies={'http': 'my.proxy.server:8080'})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/site-packages/requests/api.py", line 55, in get
    return request('get', url, **kwargs)
  File "/usr/lib/python2.6/site-packages/requests/api.py", line 44, in request
    return session.request(method=method, url=url, **kwargs)
  File "/usr/lib/python2.6/site-packages/requests/sessions.py", line 279, in request
    resp = self.send(prep, stream=stream, timeout=timeout, verify=verify, cert=cert, proxies=proxies)
  File "/usr/lib/python2.6/site-packages/requests/sessions.py", line 374, in send
    r = adapter.send(request, **kwargs)
  File "/usr/lib/python2.6/site-packages/requests/adapters.py", line 206, in send
    raise ConnectionError(sockerr)
requests.exceptions.ConnectionError: [Errno 22] Invalid argument
>>> r = requests.get("http://yum.mariadb.org/5.5/rhel6-amd64/repodata/repomd.xml", proxies={'http': 'http://my.proxy.server:8080'})
>>> 

Please see http://www.python-requests.org/en/latest/user/advanced/  (Proxies section)