Description:
------------
When using the soap extension to expose a certain class and setting the persistence to SOAP_PERSISTENCE_SESSION, PHP crashes when I throw an Exception.

Reproduce code:
---------------
<?php
class test1 {
	function soapFunction($param) {
		throw new Exception("something went wrong");
		return "blaat aap: ". $param;
	}
}
if($_GET["type"]=="server") {
	$server = new SOAPServer(null, array("uri"=> "http://some.example.uri/"));
	$server->setClass("test1");
	$server->setPersistence(SOAP_PERSISTENCE_SESSION);
	$server->handle();
} else { //client
	$client = new SOAPClient(null, array('location' => 'http://'.$_SERVER["HTTP_HOST"].$_SERVER["SCRIPT_NAME"].'?type=server', 'uri'=> 'http://some.example.uri/'));
	$res = $client->__call("soapFunction", array("hey!"));
	var_dump($res);
}
?>

Expected result:
----------------
Fatal error: Uncaught SoapFault exception: [Client] looks like we got no XML document in f:\myweb\contentarea\tests\bug_exception.php:15 Stack trace: #0 f:\myweb\contentarea\tests\bug_exception.php(15): SoapClient->__call('soapFunction', Array) #1 {main} thrown in f:\myweb\contentarea\tests\bug_exception.php on line 15

Actual result:
--------------
PHP / Apache crash