[ticket/11015] Make DBAL classes autoloadable

PHPBB3-11015

This allows us to just create the object without having to include the
driver first. However, it also means that users must specify the full
class name in config.php

tests/session/testable_factory.php

@@ -62,7 +62,7 @@ class phpbb_session_testable_factory
 	* @param dbal $dbal The database connection to use for session data
 	* @return phpbb_mock_session_testable A session instance
 	*/
-	public function get_session(dbal $dbal)
+	public function get_session(phpbb_db_driver $dbal)
 	{
 		// set up all the global variables used by session
 		global $SID, $_SID, $db, $config, $cache, $request;