Handle ObjectSpin* packets to spin physical prims on Ctrl+Shift+Drag

Addresses Mantis #3381

The current implementation works as expected if the object has no rotation or 
only rotation around the Z axis; you can spin the object left or right (around
the world Z axis).

It works a little unexpectedly if the object has a non-Z-axis rotation; in this
case the body is spun about its local Z axis, not the world Z-axis. (But SL 
also behaves oddly with a spin on an arbitrarily rotated object.)

OpenSim/Region/Framework/Scenes/SceneObjectPart.cs

@@ -176,6 +176,11 @@ namespace OpenSim.Region.Framework.Scenes
         public bool VolumeDetectActive = false; // XmlIgnore set to avoid problems with persistance until I come to care for this
                                                 // Certainly this must be a persistant setting finally
 
+        [XmlIgnore]
+        public bool IsWaitingForFirstSpinUpdatePacket = false;
+        [XmlIgnore]
+        public Quaternion SpinOldOrientation = new Quaternion();
+
         /// <summary>
         /// This part's inventory
         /// </summary>