Add debug ability to ignore reliably sent packets that are not acknowledged.

This is controlled via the console command "debug lludp client set process-unacked-sends true [<avatar-first-name> <avatar-last-name>]"
For debug purposes to see if this process for very bad connections is causing general outbound udp processing delays.
Relates to http://opensimulator.org/mantis/view.php?id=7393

OpenSim/Region/ClientStack/Linden/UDP/LLUDPClient.cs

@@ -119,8 +119,15 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         public readonly uint CircuitCode;
         /// <summary>Sequence numbers of packets we've received (for duplicate checking)</summary>
         public readonly IncomingPacketHistoryCollection PacketArchive = new IncomingPacketHistoryCollection(200);
+
+        /// <summary>
+        /// If true then we take action in response to unacked reliably sent packets such as resending the packet.
+        /// </summary>
+        public bool ProcessUnackedSends { get; set; }
+
         /// <summary>Packets we have sent that need to be ACKed by the client</summary>
         public readonly UnackedPacketCollection NeedAcks = new UnackedPacketCollection();
+
         /// <summary>ACKs that are queued up, waiting to be sent to the client</summary>
         public readonly OpenSim.Framework.LocklessQueue<uint> PendingAcks = new OpenSim.Framework.LocklessQueue<uint>();
 
@@ -225,6 +232,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             if (maxRTO != 0)
                 m_maxRTO = maxRTO;
 
+            ProcessUnackedSends = true;
+
             // Create a token bucket throttle for this client that has the scene token bucket as a parent
             m_throttleClient 
                 = new AdaptiveTokenBucket(