Re-routed session verifications, solved errors.

1) Re-routed existing session verification from auth server to api server (lib/User.php).
2) Hopefully solved 'page expired' error on buy-sell.php.
3) Fixed error on lib/Lang.php that was causing warnings to be logged to server log files.

*** REQUIRES *** 
1) Changing the cfg.php file as in the example file.
2) Running db update to v 1.03.