Theres always diff utilities. But for 0.2.1 to 0.2.2 its a bit awkward as every single file has been modified due to coding style updates.
Off the top of my head however the only files that have code changes are: Bot.php, AOChat.php, modules/TowerAttack.php and modules/AlienAttack_GUILD.php.
I try to keep the changelog accurate as an indicator, in addition, SVN commands are available for easily determining changed files (of all subsequent releases since i don't plan on changing coding style often)