Description:
------------
When 'register_long_arrays' is enabled and a session variable is unset within a foreach loop over $_SESSION the session is not written out anymore, causing the changes to the session beeing lost. (session_unregister works nice btw.)

Reproduced on various (patched and vanilla) 5.* (including 5.2.0) versions on GNU/Linux

Some debugging showed that actually the internal pointer (in ps_globals' http_session_vars zval) to the session hashtable are wrecked when doing this so this seems not to be a ext/session issue but more of a core issue.

----
Dump in php_session_flush:
gdb> print (*ps_globals.http_session_vars).value
$5 = {lval = 0x5a5a5a5a, dval = 1.7838867517321418e+127, str = {val = 0x5a5a5a5a <Address 0x5a5a5a5a out of bounds>, len = 0x5a5a5a5a}, ht = 0x5a5a5a5a, obj = {handle = 0x5a5a5a5a, handlers = 0x5a5a5a5a}}

Reproduce code:
---------------
<?php
session_start();

var_dump($_SESSION);

$_SESSION['test'] = 'blubb';
$_SESSION['foo'] = 'test';

foreach($_SESSION as $key => $val) {
        unset($_SESSION['test']);
}

var_dump($_SESSION);
?>


Expected result:
----------------
On first run:
array(9) {
}
array(1) {
  ["foo"]=>
  string(4) "test"
}

On second run:
array(1) {
  ["foo"]=>
  string(4) "test"
}
array(1) {
  ["foo"]=>
  string(4) "test"
}

Actual result:
--------------
On every run:
array(9) {
}
array(1) {
  ["foo"]=>
  string(4) "test"
}