Description:
------------
In a Windows environment, RecursiveDirectoryIterator will treat 
symlinked directories as valid directories, descending into them 
accordingly. However on Linux this isn't the case, with a symlink being 
treated as a file (leaf). 

Reproduce code:
---------------
<?php
// create a 'proper' directory with a file
mkdir('new_dir');
file_put_contents('new_dir/test.txt', 'test');

// create a symlink to our directory
symlink('new_dir', 'symlink_dir');

$iterator = new RecursiveIteratorIterator(new RecursiveDirectoryIterator(__DIR__));

foreach($iterator as $object) {
    echo $object->getFilename() . "\n";
}

Expected result:
----------------
On Windows Vista, I get this (executed in file test.php):

test.txt
test.txt
test.php

Which I would expect; the symlinked directory is treated as a regular 
directory, so the test file appears twice.


Actual result:
--------------
On Linux (same scenario):

test.php
symlink_dir
test.txt
.
..
.
..

The symlinked directory appears, but as a leaf; the contents of the 
directory are not discovered.