Other changes to extensions

Changes in extension behavior, and new features:

• mysqli - mysqli_result now implements Traversable

• pdo_mysql - Removed support for linking with MySQL client libraries older than 4.1

• The MySQL extensions mysql, mysqli and PDO_mysql use mysqlnd as the default library now. It is still possible to use libmysqlclient by specifying a path to the configure options.

• mysqlnd - Added named pipes support