Better error message for DNS exceptions on mono.

src/NzbDrone.Common/Http/Dispatchers/ManagedHttpDispatcher.cs

@@ -72,10 +72,22 @@ namespace NzbDrone.Common.Http.Dispatchers
                 httpWebResponse = (HttpWebResponse)e.Response;
 
                 if (httpWebResponse == null)
+                {
+                    // The default messages for WebException on mono are pretty horrible.
+                    if (e.Status == WebExceptionStatus.NameResolutionFailure)
+                    {
+                        throw new WebException($"DNS Name Resolution Failure: '{webRequest.RequestUri.Host}'", e.Status);
+                    }
+                    else if (OsInfo.IsNotWindows)
+                    {
+                        throw new WebException($"{e.Message}: '{webRequest.RequestUri}'", e.Status);
+                    }
+                    else
                     {
                         throw;
                     }
                 }
+            }
 
             byte[] data = null;