Fix: ETag-Values MUST be quoted according to W3C spec

MediaBrowser.Server.Implementations/HttpServer/HttpResultFactory.cs

@@ -275,7 +275,7 @@ namespace MediaBrowser.Server.Implementations.HttpServer
         /// <returns>System.Object.</returns>
         private object GetCachedResult(IRequest requestContext, IDictionary<string, string> responseHeaders, Guid cacheKey, string cacheKeyString, DateTime? lastDateModified, TimeSpan? cacheDuration, string contentType)
         {
-            responseHeaders["ETag"] = cacheKeyString;
+            responseHeaders["ETag"] = string.Format("\"{0}\"", cacheKeyString);
 
             if (IsNotModified(requestContext, cacheKey, lastDateModified, cacheDuration))
             {