Don't try to save changed attachment states when an NPC with attachments is removed from the scene.

This is done by introducing a PresenceType enum into ScenePresence which currently has two values, User and Npc.
This seems better than a SaveAttachments flag in terms of code comprehension, though I'm still slightly uneasy about introducing these semantics to core objects

OpenSim/Framework/IScene.cs

@@ -72,10 +72,11 @@ namespace OpenSim.Framework
 
         /// <summary>
         /// Register the new client with the scene.  The client starts off as a child agent - the later agent crossing
-        /// will promote it to a root agent during login.
+        /// will promote it to a root agent.
         /// </summary>
-        /// <param name="client"></param        
-        void AddNewClient(IClientAPI client);
+        /// <param name="client"></param>
+        /// <param name="type">The type of agent to add.</param>
+        void AddNewClient(IClientAPI client, PresenceType type);
 
         /// <summary>
         /// Remove the given client from the scene.

OpenSim/Framework/PresenceType.cs

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) Contributors, http://opensimulator.org/
+ * See CONTRIBUTORS.TXT for a full list of copyright holders.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the OpenSimulator Project nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+using System;
+
+namespace OpenSim.Framework
+{
+    /// <summary>
+    /// Indicate the type of ScenePresence.
+    /// </summary>
+    public enum PresenceType
+    {
+        User,
+        Npc
+    }
+}