Blacklisting improvements

New: New releases that fail will be retried a second time after waiting 1hr (configurable)
Fixed: Blacklisting releases with the same date and vastly different ages

src/NzbDrone.Core/Download/IDownloadClient.cs

@@ -11,6 +11,7 @@ namespace NzbDrone.Core.Download
         IEnumerable<HistoryItem> GetHistory(int start = 0, int limit = 0);
         void RemoveFromQueue(string id);
         void RemoveFromHistory(string id);
+        void RetryDownload(string id);
         void Test();
     }
 }