Description:
------------
stream_context_create dont overwrite HTTP headers. I'm trying to overwrite my content-type, but its not being overwrited.

Test script:
---------------
arrHttpHeaders = array(
	'http' => array(
	'header' => 'Content-Type: application/soap+xml; charset=utf-8\r\n
		     Warning: Test warning'
	)
);
$streamContext = stream_context_create($arrHttpHeaders);
				
$arrConfig = array_merge(
	self::getSoapClientConfiguration(), 
	array(
	    'local_cert' => self::getAuthCertificatePath(),
	    'passphrase' => self::getAuthCertificatePassphrase(),
	    'stream_context' => $streamContext
        )
);
				
self::$objSoapClient = new SoapClient(
	self::getSoapClientWsdlPath(), 
	$arrConfig
);

Expected result:
----------------
POST **** HTTP/1.1
Host: ****
Connection: Keep-Alive
User-Agent: PHP-SOAP/5.5.16
Content-Type: application/soap+xml; charset=utf-8
SOAPAction: ***
Content-Length: 234
Warning: Test warning

Actual result:
--------------
POST **** HTTP/1.1
Host: ****
Connection: Keep-Alive
User-Agent: PHP-SOAP/5.5.16
Content-Type: text/xml; charset=utf-8
SOAPAction: ***
Content-Length: 234
Warning: Test warning