Description:
------------
When using a proxy, the PHP Curl wrapper does not allow the user to remove or modify the Proxy-Connect header. PHP cURL will set a hard-coded "Proxy-Connect: Keep-alive" value, no matter if the user requests to disable this behavior by setting the header to null. Additionally, if the user would like to set "Proxy-Connect" to "Closed", this is impossible as cURL will still send the "Keep-Alive" header and append "Closed" afterwards, like so:
"Proxy-Connect: Keep-alive, Closed"

Test script:
---------------
<?php
//Proxy-Connection is not set, desired behavior is to remove this header from the request. The command line version of cURL does so properly, but PHP still sends it.
$headers = array('Proxy-Connection:');            

$ch = curl_init();
curl_setopt($ch, CURLOPT_PROXY, $GLOBALS['proxyserver']);
curl_setopt($ch, CURLOPT_URL, "http://www.xhaus.com/headers");
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$result = curl_exec($ch);
var_dump($result);

?>

Expected result:
----------------
HTTP Header*	Value
Accept	*/*
Connection	close
Host	www.xhaus.com
User-Agent	Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:25.0) Gecko/20100101 Firefox/29.0


Actual result:
--------------
HTTP Header*	Value
Accept	*/*
Connection	close
Host	www.xhaus.com
Proxy-Connection	Keep-Alive
User-Agent	Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:25.0) Gecko/20100101 Firefox/29.0