Validation on global settings

[Bartjan Hoogenbosch]

As you can modify the select box options within the global settings, a mistake or typo means a lockout as the page itself does the same from the config.php file, e.g.
explode(',', $config['global']['show_lines']);

The page will be unavailable if the string itself entered by the user has a fault so explode can not do its work. The only workaround is to get into MySQL and revert the change.

Validation must be done on at least the select options, but preferably on all items.