On error, dump the feed we tried to parse

Try to give more diagnostic information when a feed fails to be parsed.
This can be used to troubleshoot code later.

tornadonews/tornadonews.py

@@ -302,8 +302,13 @@ class FeedFetcher(object):
                 parsed = feedparser.parse(body)
 
                 # Extract the entries from the feed
+                try:
                     entries = list(map(partial(FeedEntry.from_entry, name),
                         parsed['entries']))
+                except:
+                    self._log.error('Unhandled exception parsing entries:\n%s',
+                        yaml.dump(parsed, default_flow_style=False))
+                    raise
 
             if not cached and (cache_dir is not None):
                 cache_out = yaml.safe_dump([e.raw for e in entries])