Some options to correct problems with dowloading from RSS would be helpful, specifically:
1.Configurable retries if NZB is empty or otherwise unavailable or invalid.
2. Restore the delay between downloads from RSS (removed in 0.28.1), this time with configurable time. Could help with e.g. tvnzb.com choking on requests.
3. Keep connection alive for longer, where sites are very slow to serve NZBs (e.g. nzbs.org sometimes).
etc.
