Description:
------------
MySQLi connection is broken when using a custom session handler. When using MySQL extension there is no problem.

Reproduce code:
---------------
<?php
$GLOBALS["DB"] = mysqli_connect("localhost","root","");

session_set_save_handler("_login_session_none","_login_session_none","_login_session_none","_login_session_write","_login_session_none","_login_session_none");
session_start();

echo mysqli_query($GLOBALS["DB"],"show status")."OK\n";

function _login_session_none($param1="", $param2="") {
  return true;
}

function _login_session_write($id,$val) {
  echo mysqli_query($GLOBALS["DB"],"show status");
}
?>

Expected result:
----------------
Object id #2OK
Object id #2O

Actual result:
--------------
Object id #2OK
Warning: mysqli_query() [function.mysqli-query]: Couldn't fetch mysqli in H:\sgs\src\test_mysqli.php on line 14