Fixes login issues for some PHP flavors.

Without this fix, some versions of PHP will create this error log: 

[26-Sep-2013 16:34:22 UTC] PHP Warning:  require(includes/classes/db/mysql/query_factory.php): failed to open stream: No such file or directory in /var/www/html/demo_160/includes/functions/sessions.php on line 60
[26-Sep-2013 16:34:22 UTC] PHP Stack trace:
[26-Sep-2013 16:34:22 UTC] PHP   1. _sess_write() /var/www/html/demo_160/includes/functions/sessions.php:0
[26-Sep-2013 16:34:22 UTC] PHP Fatal error:  require(): Failed opening required 'includes/classes/db/mysql/query_factory.php' (include_path='.:/usr/share/pear:/usr/share/php') in /var/www/html/demo_160/includes/functions/sessions.php on line 60
[26-Sep-2013 16:34:22 UTC] PHP Stack trace:
[26-Sep-2013 16:34:22 UTC] PHP   1. _sess_write() /var/www/html/demo_160/includes/functions/sessions.php:0