Description:
------------
The behavior of strtotime() on 64 bit machines (see below) for all-zero timestamps is undesirable.  On 32 bit machines the function outputs NULL for a string input "0000-00-00 00:00", on 64 bit machines it yields -62169987600.  This is undesirable, as the all-zero timestamp is not a valid date ("00" is not a month). On 64 bit systems strtotime() should return NULL for "0000-00-00 00:00".


Test script:
---------------
/* Linux ubuntu64-vbox 2.6.38-8-server #42-Ubuntu SMP Mon Apr 11 03:49:04 UTC 
 * 2011 x86_64 x86_64 x86_64 GNU/Linux
 * PHP 5.3.6-6~dotdeb.1 with Suhosin-Patch (cli) (built: Apr  3 2011 16:36:05) 
 */

<?php
  echo strtotime("0000-00-00 00:00");
?>

Actual result:
--------------
-62169987600