Description:
------------
When I use XML document with namespace definitions, I can't get attributes of nodes

Reproduce code:
---------------
$xml_file = 'test.xml';
$xml = simplexml_load_file($xml_file);
foreach($xml->Worksheet->attributes() as $a => $b) {
    echo $a,'="',$b,"\"\n";
}

test.xml:
<?xml version="1.0"?>
<Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet"
 xmlns:o="urn:schemas-microsoft-com:office:office"
 xmlns:x="urn:schemas-microsoft-com:office:excel"
 xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet"
 xmlns:html="http://www.w3.org/TR/REC-html40">
 <Worksheet ss:Name="English">
 </Worksheet>
</Workbook>

Expected result:
----------------
Name="English"