Submit handler to recache categories

IMPORTANT NOTE:You will need to "reconfigure" the Drigg module every time you add a category. This means going to Administer -> Drigg and hitting the "Save settings" button. This is important: Drigg creates an internal cached version of the categories, and needs to be "told" that new categories are available. So, you must go to the Drigg configuration screen if you add categories here (see below how to do that)

This wouldn't be necessary if you implement a custom submit handler that gets called after the normal submit handlers for the vocabulary form.