Submit functions should not call drupal_goto

In drupal 6, the right way to redirect a form after it got submitted changed.

As reported by the documentation:

To determine where the user should be sent after the form is processed, the _submit function can place a path or URL in $form_state['redirect'] which will be the target of a drupal_goto; every form is redirected after a submit. If you store nothing in $form_state['redirect'], the form will simply be redirected to itself after a submit. It is polite to use drupal_set_message() to explain to the user that the submission was successful.