Backend function now only gets called on init hook.

A small fix to prevent the plugin from being loaded too early.
It was giving errors:

Notice: Use of undefined constant TEMPLATEPATH - assumed 'TEMPLATEPATH' in /wp-includes/theme.php on line 131
Notice: Use of undefined constant STYLESHEETPATH - assumed 'STYLESHEETPATH' in /wp-includes/theme.php on line 131
What about using `admin_init` and then there's no need for the `!is_admin` check in the function?