Enable file transfer for spice_auto.html.

The work Pavel did on spice.html did not get fully transferred
into spice_auto.html; in particular, we need to append the xfer
div to the main area in order for file transfer to work.

This fixes that, and now drag + drop works in spice_auto.html.

spice_auto.html

@@ -168,6 +168,7 @@
                 {
                     var spice_xfer_area = document.createElement("div");
                     spice_xfer_area.setAttribute('id', 'spice-xfer-area');
+                    document.getElementById('spice-area').appendChild(spice_xfer_area);
                     document.getElementById('spice-area').addEventListener('dragover', handle_file_dragover, false);
                     document.getElementById('spice-area').addEventListener('drop', handle_file_drop, false);
                 }