Description:
------------
I'm using PDO to connect to Oracle Database. Function "$conn = new PDO(...)" connect to database and this is ok. When I use "$conn = null" connection is close, but this variable doesn`t logoff user from database. It looks like PDO is killing connection and at this moment doesn`t trigger logoff in database. 


Reproduce code:
---------------
try {
        $db = new PDO('oci:dbname='.base,login_to_database,pass_to_database);
    	$db->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
    	$db->setAttribute(PDO::ATTR_CASE,PDO::CASE_LOWER);
    	$db->setAttribute(PDO::ATTR_STRINGIFY_FETCHES, true);
    } 
    catch (PDOException $e) {
   	echo "Not connected: " . $e->getMessage();
   	exit;
    }

... ....

$db = null;