allow request header overrides

MediaBrowser.Model/Querying/ItemFields.cs

@@ -116,6 +116,11 @@ namespace MediaBrowser.Model.Querying
         /// </summary>
         Revenue,
 
+        /// <summary>
+        /// The screenshot image tags
+        /// </summary>
+        ScreenshotImageTags,
+
         /// <summary>
         /// The soundtrack ids
         /// </summary>

MediaBrowser.Model/Web/QueryStringDictionary.cs

@@ -208,7 +208,9 @@ namespace MediaBrowser.Model.Web
                 throw new ArgumentNullException("value");
             }
 
-            Add(name, string.Join(",", value.Select(v => v.ToString()).ToArray()));
+            var paramValue = string.Join(",", value.ToArray());
+
+            Add(name, paramValue);
         }
 
         /// <summary>