- Added a _nodeapi hook that in time will replace the _node hook. Trying
  to make as few changes to existing code as possible until the new api
  is stabilized.
- Modified node_form() to add administration options from other modules
  using the _nodeapi hook.
- Modified node_save() to fetch which fields should be saved to the node
  table from the _nodeapi hook.
- Moved comment and queue options from node_form() and node_save() to
  the modules _nodeapi hooks.