Description:
------------
You cannot create a SOAP header that is in no namespace. (This 
is required by the new Google Adwords SOAP API, see https://
adwords.google.com/api/adwords/v2/TrafficEstimatorService?
wsdl.)

Furthermore, the SOAPHeader class allows you to create headers 
in an empty namespace, by passing in null or "" for the 
namespace URI. This is illegal. (Unless defined as the default 
namespace.)

The extension should be changed to place these elements in no 
namespace instead.

Reproduce code:
---------------
$client=new SOAPClient(null, array('location' => 'http://localhost', 'uri' => 'myNS', 'exceptions' => false, 'trace' => true));

$header = new SOAPHeader(null, 'foo', 'bar');

$response= $client->__call('function', array(), null, $header);

print $client->__getLastRequest();


Expected result:
----------------
<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/
soap/envelope/" xmlns:ns1="myNS" xmlns:xsd="http://www.w3.org/
2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-
instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/
encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/
soap/encoding/"><SOAP-ENV:Header><foo>bar<foo></SOAP-
ENV:Header><SOAP-ENV:Body><ns1:function/></SOAP-ENV:Body></
SOAP-ENV:Envelope>


Actual result:
--------------
<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/
soap/envelope/" xmlns:ns1="myNS" xmlns:ns2="" 
xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" 
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/
encoding/"><SOAP-ENV:Header><ns2:foo>bar</ns2:foo></SOAP-
ENV:Header><SOAP-ENV:Body><ns1:function/></SOAP-ENV:Body></
SOAP-ENV:Envelope>