cloning physics objects

If a mesh has a physics body it will now be cloned together with the
mesh.
Default behavior is to clone it, the developer can choose.

src/Mesh/babylon.mesh.ts

@@ -1009,8 +1009,16 @@
         }
 
         // Clone
-        public clone(name: string, newParent?: Node, doNotCloneChildren?: boolean): Mesh {
-            return new Mesh(name, this.getScene(), newParent, this, doNotCloneChildren);
+        public clone(name: string, newParent?: Node, doNotCloneChildren?: boolean, clonePhysicsImpostor: boolean = true): Mesh {
+            var mesh = new Mesh(name, this.getScene(), newParent, this, doNotCloneChildren);
+            //physics clone
+            if(clonePhysicsImpostor && this.getScene().getPhysicsEngine()) {
+                var impostor = this.getScene().getPhysicsEngine().getImpostorForPhysicsObject(this);
+                if(impostor) {
+                    mesh.physicsImpostor = impostor.clone(mesh);
+                }
+            }
+            return mesh;
         }
 
         // Dispose

src/Physics/babylon.physicsImpostor.ts

@@ -49,13 +49,13 @@ module BABYLON {
             otherImpostor: PhysicsImpostor
         }>;
 
-        constructor(public object: IPhysicsEnabledObject, public type: number, private _options: PhysicsImpostorParameters = { mass: 0 }, scene?: Scene) {
+        constructor(public object: IPhysicsEnabledObject, public type: number, private _options: PhysicsImpostorParameters = { mass: 0 }, private _scene?: Scene) {
             //legacy support for old syntax.
-            if (!scene && object.getScene) {
-                scene = object.getScene()
+            if (!this._scene && object.getScene) {
+                this._scene = object.getScene()
             }
 
-            this._physicsEngine = scene.getPhysicsEngine();
+            this._physicsEngine = this._scene.getPhysicsEngine();
             if (!this._physicsEngine) {
                 Tools.Error("Physics not enabled. Please use scene.enablePhysics(...) before creating impostors.")
             } else {
@@ -377,6 +377,10 @@ module BABYLON {
         public wakeUp() {
             this._physicsEngine.getPhysicsPlugin().wakeUpBody(this);
         }
+        
+        public clone(newObject:IPhysicsEnabledObject) {
+            return new PhysicsImpostor(newObject, this.type, this._options, this._scene);
+        }
 
         public dispose(/*disposeChildren: boolean = true*/) {
             this.physicsBody = null;