Make compatible with Drupal core feed render

The feeds rendered by D6 core makes certain properties modifiable that Views doesn't make modifiable.

D6 core sends the same node object into hook_nodeapi('view') and hook_nodeapi('alter') that is used to render the rss items. It also sets the link prior on the node object prior to sending it to the nodeapi.

The way D6 core works makes it possible to modify the link as well as other data on the node that isn't possible to modify in views_plugin_row_node_rss.