Description:
------------
Using XPath to return values for attributes with a namespace does not work. It seems to be dropping any namespaces for attributes when using XPath. But the namespace is clearly registered because it can be used to access nodes, when using XPath.

Reproduce code:
---------------
$xml =<<<XML
<xml xmlns:a="http://a">
    <data a:label="I am A" label="I am Nothing">test1</data>
    <a:data a:label="I am a:A" label="I am a:Nothing">test2</a:data>
</xml>
XML;

$x = simplexml_load_string($xml);
$x->registerXPathNamespace("a", "http://a");

var_dump($x->xpath("/xml/data/@a:label"));
echo "<br /><br />";
var_dump($x->xpath("/xml/a:data"));
echo "<br /><br />";
var_dump($x->xpath("/xml/a:data/@a:label"));
echo "<br /><br />";
var_dump($x->data->attributes("http://a"));

Expected result:
----------------
array(1) { [0]=>  object(SimpleXMLElement)#2 (1) { ["@attributes"]=>  array(1) { ["label"]=>  string(12) "I am A" } } }

array(1) { [0]=> object(SimpleXMLElement)#2 (2) { ["@attributes"]=> array(1) { ["label"]=> string(14) "I am a:Nothing" } [0]=> string(5) "test2" } }

array(1) { [0]=> object(SimpleXMLElement)#2 (1) { ["@attributes"]=> array(1) { ["label"]=> string(14) "I am a:A" } } } 

object(SimpleXMLElement)#4 (1) { ["@attributes"]=> array(1) { ["label"]=> string(6) "I am A" } }

Actual result:
--------------
array(1) { [0]=>  object(SimpleXMLElement)#2 (1) { ["@attributes"]=>  array(1) { ["label"]=>  string(12) "I am Nothing" } } }

array(1) { [0]=> object(SimpleXMLElement)#2 (2) { ["@attributes"]=> array(1) { ["label"]=> string(14) "I am a:Nothing" } [0]=> string(5) "test2" } }

array(1) { [0]=> object(SimpleXMLElement)#2 (1) { ["@attributes"]=> array(1) { ["label"]=> string(14) "I am a:Nothing" } } }

object(SimpleXMLElement)#4 (1) { ["@attributes"]=> array(1) { ["label"]=> string(6) "I am A" } }