Description:
------------
When you request the ReflectionParameters for the PDO constructor, it returns an empty array instead of an array of ReflectionParamters representing the dsn, username, password and driver options.

It would seem that PDO is not providing Reflection info for it's constructor (possibly more).

Reproduce code:
---------------
$method = new ReflectionMethod ('PDO', '__construct');
print_r ($method->getParameters ());

Expected result:
----------------
Array
(
    [0] => ReflectionParameter Object
        (
            [name] => dsn
        )

    [1] => ReflectionParameter Object
        (
            [name] => username
        )

    [2] => ReflectionParameter Object
        (
            [name] => password
        )

    [3] => ReflectionParameter Object
        (
            [name] => driver_options
        )

)

Actual result:
--------------
Array
(
)