Fix "Undefined index: smarty_debug" notices generated by includes/template.inc.php

The default includes/config.php omits specifying $config['smarty_debug'] this results in PHP notices such as:

    PHP Notice:  Undefined index: smarty_debug in /var/www/example.com/includes/template.inc.php on line 15
    PHP Stack trace:
    PHP   1. {main}() /var/www/example.com/public/login.php:0
    PHP   2. include() /var/www/example.com/public/login.php:2
    PHP   3. require_once() /var/www/example.com/includes/base.inc.php:11

for every request.  This trivial patch includes a sensible default and prevents this notices.