docs: def geturl(urllib2_resp):
      """
      Use instead of urllib.addinfourl.geturl(), which appears to have
      some issues with dropping the double slash for certain schemes
      (e.g. file://).  This implementation is probably over-eager, as it
      always restores '://' if it is missing, and it appears some url
      schemata aren't always followed by '//' after the colon, but as
      far as I know pip doesn't need any of those.
      The URI RFC can be found at: http://tools.ietf.org/html/rfc1630
  
      This function assumes that
          scheme:/foo/bar
      is the same as
          scheme:///foo/bar
      """
      url = urllib2_resp.geturl()
      scheme, rest = url.split(':', 1)
      if rest.startswith('//'):
          return url
      else:
          # FIXME: write a good test to cover it
          return '%s://%s' % (scheme, rest)