* Make the parent widget of the edit form a custom container element,

* Make the parent widget of the edit form a custom container element,
  so that we can have a nice value callback in order to separate
  form structure and result value (as CCK widgets are inside a '#tree').

* Convert filefield back to CCK multiple value handling, replacing the
  "Delete" checkbox with a "Delete" button and storing the previous file
  as temporary property of the new one, until the node is submitted.