add hook_form_process_success to drupal_form_process

Right now, after a successful form submission, Drupal always does either a redirect (most common) or rebuilds the form (if #redirect is set to FALSE). For Ajax form submission, this is not enough choices. There needs to be someway to override this behavior. I am proposing the addition of a hook before the drupal_form_redirect in drupal_form_process.
This hook used to be part of #193311: Ajax Popups in Drupal 7: Adding Modal Dialogs to Help, Confirmations and Filter tips (Unified) and, along with a drupal_goto patch soon to be submitted, forms a basis of adding more power to #374646: Popbox (Popups Lite): Adding Modal Dialogs to Confirmations.