Description:
------------
If you try to get an url via a proxy with authentication, curl sends a "Server auth" header instead of "Proxy Auth", making authentication impossible.
If you try to get the same page using curl binary, the result is the expected one. The curl command corresponding to php reproduce code is:

curl -v -xexample.org:80 -Ufoo:bar -o /dev/null http://www.google.com

Reproduce code:
---------------
<?php

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://php.net');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_PROXY, 'http://example.org:80');
curl_setopt($ch, CURLOPT_PROXYAUTH, CURLAUTH_BASIC); 
curl_setopt($ch, CURLOPT_USERPWD, 'foo:bar');
curl_setopt($ch, CURLOPT_VERBOSE, true);
curl_exec($ch);


Expected result:
----------------
* About to connect() to proxy example.org port 80 (#0)
*   Trying 208.77.188.166... * connected
* Connected to example.org (208.77.188.166) port 80 (#0)
* Proxy auth using Basic with user 'foo'
> GET http://php.net HTTP/1.1
Authorization: Basic Zm9vOmJhcg==
Host: php.net
Pragma: no-cache
Accept: */*
Proxy-Connection: Keep-Alive

[...]

Actual result:
--------------
* About to connect() to proxy example.org port 80 (#0)
*   Trying 208.77.188.166... * connected
* Connected to example.org (208.77.188.166) port 80 (#0)
* Server auth using Basic with user 'foo'
> GET http://php.net HTTP/1.1
Authorization: Basic Zm9vOmJhcg==
Host: php.net
Pragma: no-cache
Accept: */*
Proxy-Connection: Keep-Alive

[...]