Description:
------------
It seems that if an Exception object is serialized and unserialized, the resulting object does not have the private "previous" property set correctly.

Invoking the __toString method on the resulting object generates a PHP Notice.



Test script:
---------------
<?php
$e1 = new Exception("Test");
$e2 = unserialize( serialize( $e1 ) );
echo $e2->__toString() . "\n";
?>


Expected result:
----------------
exception 'Exception' with message 'Test' in /home/...php:2
Stack trace:
#0 {main}


Actual result:
--------------
PHP Notice:  Undefined property: Exception::$previous in /home/...php on line 4
PHP Stack trace:
PHP   1. {main}() /home/...php:0
PHP   2. Exception->__toString() /home/...php:4
exception 'Exception' with message 'Test' in /home/...php:2
Stack trace:
#0 {main}