A few updates necessary for load balancer.

- handle GetUser request for nonexistent user gracefully
- include throttle levels in ClientInfo
- code to save/restore throttles in client stack
- only update/send updates to active clients
- make animation classes serializable

OpenSim/Region/Framework/Scenes/Animation.cs

@@ -25,11 +25,13 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+using System;
 using OpenMetaverse;
 using OpenMetaverse.StructuredData;
 
 namespace OpenSim.Region.Framework.Scenes
 {
+    [Serializable]
     public class Animation
     {
         private UUID animID;