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/DownloadClientBase.cs

@@ -43,6 +43,7 @@ namespace NzbDrone.Core.Download
         public abstract IEnumerable<HistoryItem> GetHistory(int start = 0, int limit = 10);
         public abstract void RemoveFromQueue(string id);
         public abstract void RemoveFromHistory(string id);
+        public abstract void RetryDownload(string id);
         public abstract void Test();
     }
 }