Assignment type plugins unable to preprocess forms in Moodle 2.0 [patch]

If you add a 'filemanager' form element to the 'settings' form for a module, you need to be able to pre-process the form data to set up the draft area where the newly uploaded files will be stored.

The assignment type plugin interface does not currently allow this to be done, which is causing problems when I am trying to update my uploadpdf plugin type to Moodle 2.0 (as this includes a filemanager element to allow a coversheet to be uploaded, to be attached to all the students' assignments).

I have attached a proposed patch which would enable this functionality (as well as allowing for extra validation of the form, if so required).

Please could someone take a look at this and include it in Moodle 2.0, if it is suitable (or suggest a better solution, if this is not going to work)?