Fail on http errors (>=300) for cURL downloads.

As per https://github.com/masroore/CurlSharp/blob/f9da9aefbc2e26e7ad9e1a242a45e9277b1fc82d/CurlSharp/Enums/CurlOption.cs#L224-L229.
This should prevent download errors being concealed.

Core/Net/Net.cs

@@ -243,37 +243,37 @@ public static string DownloadText(Uri url, string authToken = "")
 
  return agent.DownloadString(url.OriginalString);
  }
- catch (Exception)
+ catch (Exception e)
  {
- try
- {
- log.InfoFormat("Download failed, trying with curlsharp...");
+ log.InfoFormat(e.ToString());
+ log.InfoFormat("Download failed, trying with curlsharp...");
 
-  var content = string.Empty;
+ var content = string.Empty;
 
-  var client = Curl.CreateEasy(url.OriginalString, delegate (byte[] buf, int size, int nmemb, object extraData)
-  {
-  content += Encoding.UTF8.GetString(buf);
-  return size * nmemb;
-  });
+ var client = Curl.CreateEasy(url.OriginalString, delegate (byte[] buf, int size, int nmemb, object extraData)
+ {
+ content += Encoding.UTF8.GetString(buf);
+ return size * nmemb;
+ });
 
- using (client)
- {
- var result = client.Perform();
+ client.SetOpt(CurlOption.FailOnError, true);
+
+ using (client)
+ {
+ var result = client.Perform();
+ var returnCode = client.ResponseCode;
 
- if (result != CurlCode.Ok)
- {
- throw new Exception("Curl download failed with error " + result);
- }
+ if (result != CurlCode.Ok)
+ {
+ throw new WebException(
+ String.Format("Curl download failed with error {0} ({1})", result, returnCode), 
+ e
+ );
+ }
 
-  log.DebugFormat("Download from {0}:\r\n\r\n{1}", url, content);
+ log.DebugFormat("Download from {0}:\r\n\r\n{1}", url, content);
 
- return content;
- }
- }
- catch (Exception e)
- {
- throw new Kraken("Downloading using cURL failed", e);
+ return content;
  }
  }
  }