Description:
------------
When subclassing PDO from different classes, all the classes become the last instantiated.

This happens in the Debian etch packages (php5 5.2.0-8+etch1) and in CentOS release 4.4 (php5 5.2.0-10 built from fedora SRPM)

Reproduce code:
---------------
class CA extends PDO {
  public $a=1;
  public function __construct() {
    parent::__construct("mysql:dbname=dbname", "user", "password",array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8'",PDO::ATTR_PERSISTENT => true));
  }
}

class CB extends PDO {
  public $b=2;
  public function __construct() {
    parent::__construct("mysql:dbname=dbname", "user", "password",array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8'",PDO::ATTR_PERSISTENT => true));
  }
}
$a = new CA();
$b = new CB();
print_r($a);
print_r($b);


Expected result:
----------------
CA Object
(
     [a] => 1
)


CB Object
(
     [b] => 2
)


Actual result:
--------------
CB Object
(
     [b] => 2
)


CB Object
(
     [b] => 2
)