The aggregate plugin's handling of http 301 (moved permanently) could be improved. Per RFC 1945:
The requested resource has been assigned a new permanent URL and any future references to this resource should be done using that URL.
So ideally aggregate would notice the 301 and use the new url henceforth.
It's a little tricky because the aggregate plugin can't just edit the page and change the url in the preprocessor directive. (Because committing such an edit would be .. hard.) Also, aggregate directives may also include a separate url for the site, which may also have changed. Perhaps the thing to do is record the new url in the aggregate plugin's state file, and change the message to "Processed ok (new url http://..)", and let the user deal with updating the page later.
Assuming they really mean 301 (because 401 is "Unauthorized"), I've updated the body of the text but the page itself should really be renamed. -- adam.