Description:
------------
If you json encode a simplexml object, any xml leaf nodes will lose 
their attributes

The attached script has two small xml strings.  One with attributes 
on the leaf node, one without.

When you run the script, attribute values disappear for the second 
json string 

Reproduce code:
---------------
<?php
$xml_string1 = '<?xml version="1.0"?><ItemList><Item ID="456"><ExtraTag>ABC</ExtraTag></Item><Item ID="789"><ExtraTag>DEF</ExtraTag></Item></ItemList>';
$xml_string2 = '<?xml version="1.0"?><ItemList><Item ID="456">ABC</Item><Item ID="789">DEF</Item></ItemList>';
$xml_obj = simplexml_load_string($xml_string1);
$json = json_encode($xml_obj);
print "Input XML Document: " . htmlentities($xml_string1) . "<br/>attributes are present:<br/>$json<br/><br/>";

$xml_obj = simplexml_load_string($xml_string2);
$json = json_encode($xml_obj);
print "Input XML Document: " . htmlentities($xml_string2) . "<br/>attributes are <b>Not</b> present:<br/>$json<br/><br/>";
phpinfo();
?>

Expected result:
----------------
Input XML Document: <?xml version="1.0"?><ItemList><Item 
ID="456"><ExtraTag>ABC</ExtraTag></Item><Item 
ID="789"><ExtraTag>DEF</ExtraTag></Item></ItemList>

attributes are present:
{"Item":[{"@attributes":{"ID":"456"},"ExtraTag":"ABC"},{"@attributes"
:{"ID":"789"},"ExtraTag":"DEF"}]}

Input XML Document: <?xml version="1.0"?><ItemList><Item 
ID="456">ABC</Item><Item ID="789">DEF</Item></ItemList>

attributes are Not present:
{"Item":["ABC","DEF"]}

Actual result:
--------------
json string above labeled with "attributes are present:" is correctly 
json encoded.

json string above labeled with "attributes are Not present:" is 
incorrectly json encoded.  The json object does not have the 
attribute name or values