Description:
------------
If I add create a global variable array which contains recursive entries it causes PHP to crash when I register it by calling session_register. This appears to be because the PS_ENCODE_LOOP macro does not check for recursion.


Reproduce code:
---------------
<?php

$array = array();

$array["foo"] = NULL;
$array["bar"] = NULL;
$array["guff"] = NULL;
$array["blah"] = &$array;

var_dump(session_start());
var_dump(session_register($array));
echo "Done!\n";
?>


Expected result:
----------------
Perhaps we should check for recusion rather like the JSON extension does (see json_encode_array() in JSON.c)?

Actual result:
--------------
bool(true)