Description:
------------
SimpleXML objects should implement the Countable interface in order to work properly with the count() function.

The comments of bug #30113, "ArrayAccess interface does not implement count functionality", imply that the Countable interface appears in PHP 5.1 and is not yet available in 5.0.2. Therefore, the behaviour of the repro code below (returning 1 for count() instead of 3) is not a bug for 5.0.2, since it is expected behaviour for count() to return 1 when given an object as its parameter. However, given the pseudo-array nature of a SimpleXML object, a count() of 3 would be very convenient indeed in many situations.

I was unable to find a mention of Countable getting implemented for SimpleXML objects in 5.1, so I'm submitting this request for consideration.

(Note: in the code below, there would naturally be trivial ways to get a proper count for the $xml->wibblet->somesuch elements, but the code is meant to merely illustrate the described issue.)

Reproduce code:
---------------
<?php
$xmlstr = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<testdata>
  <wibblet>
     <somesuch>random data</somesuch>
     <somesuch>more random data</somesuch>
     <somesuch>not that random</somesuch>
  </wibblet>
</testdata>
XML;
$xml = simplexml_load_string($xmlstr);
foreach($xml->wibblet->somesuch as $somesuch) {
   echo $somesuch;
   echo "<br />";
}
echo "Count: " . count($xml->wibblet->somesuch);
?>

Expected result:
----------------
random data
more random data
not that random
Count: 3

Actual result:
--------------
random data
more random data
not that random
Count: 1