This patch extends urllib.urlopen() so that
proxies may be specified explicitly.  This is
achieved by adding an optional "proxies"
parameter.  If this parameter is omitted,
urlopen() acts exactly as before, ie gets
proxy settings from the environment.

This is useful if you want to tell urlopen()
not to use the proxy: just pass an empty
dictionary.

Also included is a patch to the urllib
documentation explaining the new parameter.

Apologies if patch format is not exactly as
required: this is my first submission.  All
feedback appreciated.  :-)