Support for embedded media fields

The following patch adds support for emimage, emvideo, and emaudio CCK fields added to nodes with the Embedded Media Field module. A similar approach would likely work for other media types supported by that module but these are all I've personally tested.

To import these fields, you only need to supply the URL of the embedded media (for example, the URL of an image hosted on Picasa or Flickr, or a video hosted on YouTube). All other fields are determined by the emfield module, just as when creating or editing a node via the standard Drupal web interface.