Description:
------------
SoapHeader::mustUnderstand are ignore in SoapServer context

Test script:
---------------
<?php
	class Tool{
		public function TOKEN($id){
			return new SoapHeader('namespace1', 'TOKEN', $id, true);
		}
		public function Method(){}
	}

	$input = $input =
		'<?xml version="1.0"?>'.PHP_EOL.
		'<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="namespace1"'.
		' xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"'.
		' xmlns:xsd="http://www.w3.org/2001/XMLSchema">'.
		'<SOAP-ENV:Header><ns1:TOKEN soapenv:mustUnderstand="1">abc</ns1:TOKEN></SOAP-ENV:Header>'.
		'<SOAP-ENV:Body><ns1:Method /></SOAP-ENV:Body></SOAP-ENV:Envelope>';

	$soap = new SoapServer(null, array('uri' => '127.0.0.1'));
	$soap->setClass('Tool'); $soap->handle($input);
	$out = ob_get_contents(); ob_end_clean();

	echo $out;
?>

Expected result:
----------------
<ns1:TOKEN soapenv:mustUnderstand="1">abc</ns1:TOKEN>

Actual result:
--------------
<ns1:TOKEN>abc</ns1:TOKEN>