Description:
------------
Foreach issues warning with link to http://php.net/manual/en/function.main.php when iterating over SimpleXML object.

Test script:
---------------
<?php // oop_bug_main.php
error_reporting(E_ALL);
echo "<pre>";
$xml = <<<XML
<category id='1' title='category 1'>
  <item id='a' title='item a' delete='true' />
  <item id='b' title='item b' delete='false'>B Stays</item>
</category>
XML;
$obj = SimpleXML_Load_string($xml);
$key = 0;
foreach ($obj->item as $item) {
    $attrs = $item->attributes();
    if ($attrs['delete'] == 'true') unset($obj->item[$key]);
    $key++;
}

Expected result:
----------------
No message about function main()

Actual result:
--------------
<pre><br />
<b>Warning</b>:  main() [<a href='function.main'>function.main</a>]: Node no longer exists in <b>/Applications/MAMP/htdocs/oop_bug_main.php</b> on line <b>12</b><br />