Form submission handler for system_file_system_settings().
Adds a menu rebuild after the public file path has been changed, so that the menu router item depending on that file path will be regenerated.
function image_system_file_system_settings_submit($form, &$form_state) {
if ($form['file_public_path']['#default_value'] !== $form_state['values']['file_public_path']) {
variable_set('menu_rebuild_needed', TRUE);
}
}