Make the form callback as defined by hook_forms behave as $form[#base] in D5

Ie if my callback is called foo_form, and I define that for my bar_form_123 form in hook_forms, then I expect that foo_form_validate and _:submit be called after submitting the form.

chx says: drupal_prepare_form sets the #submit and it's blissfully unaware of how to
form came into existence. I do not think drupal_retrieve_form stores the callback in a
property. It should be easy to do so, though.