[download] improve error message

while give

```
2014-08-30 12:24 INFO     download      bt-chat.com     Downloading: Bering.Sea.Gold.Under.the.Ice.S03E02.480p.HDTV.x264-mSD
2014-08-30 12:24 WARNING  download      bt-chat.com     RequestException [Errno 1] _ssl.c:504: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed, while downloading https://torcache.net/torrent/C28D6A86369E095B7D3509D4C86C0BC09286995B.torrent
```

 instead of

 ```
 2014-08-30 12:30 INFO     download      bt-chat.com     Downloading: Bering.Sea.Gold.Under.the.Ice.S03E02.480p.HDTV.x264-mSD
2014-08-30 12:30 WARNING  download      bt-chat.com     RequestException [Errno 1] _ssl.c:504: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
```
[magnet] add zoink.it to list of torrent caches

See gh-316
Merge pull request #315 from thomasleveil/download-better-err-msg

[download] improve error message
Merge pull request #317 from thomasleveil/torrent-cache-zoink.it

[magnet] add zoink.it to list of torrent caches
make_rss handles rendering errors for the title properly
Fall back to entry title when jinja render fails in make_rss
Remove unused imports from download plugin
Make scheduler restartability less hacky
Make sure any exceptions in scheduler thread are logged
Make sure any exceptions in task_queue thread are logged