Do not call watchdog() if a redirected feed is not parseable

I've committed this to CVS HEAD. The patch didn't apply to DRUPAL-6 so I did not commit it to Drupal 6. I'll lower the version module and mark it 'code needs work'.

Probably better as 'to be ported'.

The code for D7 is now:

      // Log if feed URL has changed.
      if ($feed->url != $feed_url) {
        watchdog('aggregator', 'Updated URL for feed %title to %url.', array('%title' => $feed->title, '%url' => $feed->url));
      }

This still does not check for status 301 but if the url did change. To me it still seems wise to change the code to check for http 301 and not the url but maybe someone does know better and close this issue / set it back to D6 which still applies?