Description:
------------
if extends pdo, then visibility keyword work failure.

Reproduce code:
---------------
class test extends PDO
{
    private function isPrivate()
    {
        echo 'this is a private method.';
    }
}

$test = new test('sqlite:./test/mydb.sq3');
$test->isPrivate();
// bad output: this is a private method.

Expected result:
----------------
class test extends PDO
{
    private function isPrivate()
    {
        echo 'this is a private method.';
    }
}

$test = new test('sqlite:./test/mydb.sq3');
$test->isPrivate();
// Expected output: Fatal error: Call to private method test::isPrivate() from