To better deal with the random savefile corruptions that occur for some
users. This should help? I tested it with each file in the chain
corrupted to make sure it was falling back onto the backups properly,
and made it delete the base file if all backups were corrupt, which is a
very unlikely scenario but might as well put a case to handle it.
With this, autoloading upon launching the game should be fully working.
Also added some randomness to the pitch of step_sfx to make them sound a
bit less repetitive, and made it so the game can only save if the
current scene is a Scene_Map (because auto_saving at the titlescreen
breaks things pretty badly).
