Restore [Startup] physical_prim flag which can stop any prims being subject to physics

This had stopped working.  However, at the moment it still allows the physics flag to be set even though this has no effect.  This needs to be fixed.
Default for this flag is true as previously.

OpenSim/Framework/ConfigSettings.cs

@@ -34,7 +34,13 @@ namespace OpenSim.Framework
         public bool   See_into_region_from_neighbor { get; set; }
         public string StorageDll                    { get; set; }
         public string ClientstackDll                { get; set; }
+
+        /// <summary>
+        /// Controls whether physics can be applied to prims.  Even if false, prims still have entries in a
+        /// PhysicsScene in order to perform collision detection
+        /// </summary>
         public bool   PhysicalPrim                  { get; set; }
+        
         public string LibrariesXMLFile              { get; set; }
 
         public const uint DefaultRegionHttpPort = 9000;

OpenSim/Region/Framework/Scenes/SceneObjectPart.cs

@@ -1551,7 +1551,9 @@ namespace OpenSim.Region.Framework.Scenes
         /// <param name="m_physicalPrim"></param>
         public void ApplyPhysics(uint rootObjectFlags, bool VolumeDetectActive, bool m_physicalPrim)
         {
-//            m_log.DebugFormat("[SCENE OBJECT PART]: Applying physics to {0} {1} {2}", Name, LocalId, UUID);
+//            m_log.DebugFormat(
+//                "[SCENE OBJECT PART]: Applying physics to {0} {1}, m_physicalPrim {2}",
+//                Name, LocalId, UUID, m_physicalPrim);
 
             bool isPhysical = (((rootObjectFlags & (uint) PrimFlags.Physics) != 0) && m_physicalPrim);
             bool isPhantom = ((rootObjectFlags & (uint) PrimFlags.Phantom) != 0);
@@ -1816,6 +1818,9 @@ namespace OpenSim.Region.Framework.Scenes
         /// <param name="isNew"></param>
         public void DoPhysicsPropertyUpdate(bool UsePhysics, bool isNew)
         {
+            if (!ParentGroup.Scene.m_physicalPrim && UsePhysics)
+                return;
+
             if (IsJoint())
             {
                 DoPhysicsPropertyUpdateForNinjaJoint(UsePhysics, isNew);

bin/OpenSimDefaults.ini

@@ -173,7 +173,8 @@
     ; ## PHYSICS
     ; ##
 
-    ; if you would like to allow prims to be physical and move by physics with the physical checkbox in the client set this to true.
+    ; If true then prims can be made subject to physics (gravity, pushing, etc.).
+    ; If false then physics flag can be set but it is not honoured.  However, prims are still solid for the purposes of collision direction
     physical_prim = true
 
     ; Select a mesher here.