Document the limitation that urllib does not work with proxies which

require authenication.  This is an implementation limitation rather than
required behavior, and may be fixed in the future.

This closes SourceForge bug #111725.

Doc/lib/liburllib.tex

@@ -62,11 +62,12 @@ If the \var{url} uses the \file{http:} scheme identifier, the optional
 must in standard \file{application/x-www-form-urlencoded} format;
 see the \function{urlencode()} function below.
 
-The \function{urlopen()} function works transparently with proxies.
-In a \UNIX{} or Windows environment, set the \envvar{http_proxy},
-\envvar{ftp_proxy} or \envvar{gopher_proxy} environment variables to a
-URL that identifies the proxy server before starting the Python
-interpreter.  For example (the \character{\%} is the command prompt):
+The \function{urlopen()} function works transparently with proxies
+whicd do not require authentication.  In a \UNIX{} or Windows
+environment, set the \envvar{http_proxy}, \envvar{ftp_proxy} or
+\envvar{gopher_proxy} environment variables to a URL that identifies
+the proxy server before starting the Python interpreter.  For example
+(the \character{\%} is the command prompt):
 
 \begin{verbatim}
 % http_proxy="http://www.someproxy.com:3128"
@@ -78,6 +79,9 @@ interpreter.  For example (the \character{\%} is the command prompt):
 In a Macintosh environment, \function{urlopen()} will retrieve proxy
 information from Internet\index{Internet Config} Config.
 
+Proxies which require authentication for use are not currently
+supported; this is considered an implementation limitation.
+
 The \function{urlopen()} function works transparently with proxies.
 In a \UNIX{} or Windows environment, set the \envvar{http_proxy},
 \envvar{ftp_proxy} or \envvar{gopher_proxy} environment variables to a