added flexifield_filefield module for making filefields work inside of flexifields (no, really this time)

re-organized code and added support for multi-valued fields that use drag-and-drop+ahah to exist within a multi-valued flexifield. issue [#335490].

fixed bug with integrating widgets whose #process functions add additional form elements that have #process functions that rely on $form['#field_info'][$field_name] being available. example issue: [#357767].