Added NMA support, also added generic HttpStatusCode handling

NzbDrone.Core/Exceptions/DownstreamException.cs

@@ -0,0 +1,21 @@
+using System.Net;
+using NzbDrone.Common.Exceptions;
+
+namespace NzbDrone.Core.Exceptions
+{
+    public class DownstreamException : NzbDroneException
+    {
+        public HttpStatusCode StatusCode { get; private set; }
+
+        public DownstreamException(HttpStatusCode statusCode, string message, params object[] args) : base(message, args)
+        {
+            StatusCode = statusCode;
+        }
+
+        public DownstreamException(HttpStatusCode statusCode, string message)
+            : base(message)
+        {
+            StatusCode = statusCode;
+        }
+    }
+}