Add a way to put things at the front of the queue for any throttle group.

Adds a DoubleLocklessQueue and uses it for the outgoing buckets. Added
a flag value to the Throttle Type (again) because although it's hacky, it's
the best of a bad bunch to get the message through the UDP stack to where it's
needed.

OpenSim/Framework/LocklessQueue.cs

@@ -29,7 +29,7 @@ using System.Threading;
 
 namespace OpenSim.Framework
 {
-    public sealed class LocklessQueue<T>
+    public class LocklessQueue<T>
     {
         private sealed class SingleLinkNode
         {
@@ -41,7 +41,7 @@ namespace OpenSim.Framework
         SingleLinkNode tail;
         int count;
 
-        public int Count { get { return count; } }
+        public virtual int Count { get { return count; } }
 
         public LocklessQueue()
         {
@@ -76,7 +76,7 @@ namespace OpenSim.Framework
             Interlocked.Increment(ref count);
         }
 
-        public bool Dequeue(out T item)
+        public virtual bool Dequeue(out T item)
         {
             item = default(T);
             SingleLinkNode oldHead = null;
@@ -136,4 +136,4 @@ namespace OpenSim.Framework
                 (object)Interlocked.CompareExchange<SingleLinkNode>(ref location, newValue, comparand);
         }
     }
-}
+}

OpenSim/Framework/ThrottleOutPacketType.cs

@@ -47,6 +47,8 @@ namespace OpenSim.Framework
         Texture = 5,
         /// <summary>Non-texture assets</summary>
         Asset = 6,
+
+        HighPriority = 128,
     }
 
     [Flags]