Description:
------------
lastInsertId() always returns "0" after executing a dereferenced native (non-emulated) prepared statement. Storing the PDOStatement in a variable _then_ executing it solves that problem, and so does using emulated prepared statements.

PHP was compiled with --enable-debug --with-pdo-mysql=mysqlnd, I haven't tested with other combinations yet.

Reproduce code:
---------------
<?php
$db = new PDO('mysql:dbname=test;unix_socket=/var/run/mysqld/mysqld.sock', 'user', 'password', array(
	PDO::ATTR_EMULATE_PREPARES => false
));

$db->exec('DROP TABLE IF EXISTS test');
$db->exec('CREATE TABLE test (id INT auto_increment, PRIMARY KEY (id))');

$sql = 'INSERT INTO test (id) VALUES (NULL)';


$db->prepare($sql)->execute();
var_dump($db->lastInsertId());

$stmt = $db->prepare($sql);
$stmt->execute();
var_dump($db->lastInsertId());
?>

Expected result:
----------------
string(1) "1"
string(1) "2"

Actual result:
--------------
string(1) "0"
string(1) "2"