The urllib module does not support http proxy authentication with passwords.  The urllib2 module does, so I changed pimp.py to use urllib2.  I have tested the patch below after setting my http_proxy environment variable to the form "http://user:pass@proxy.com:1234".

It may be possible to remove the dependency on urllib entirely by sustituting a urllib2 work-alike for a call to urllib.url2pathname().

This may affect the exception(s) raised when unable to connect.  For example, PackageManager.py catches an IOError, but I believe urllib2 raises a socket.gaierror when unable to resolve the name of the URL. I have not resolved this issue.