more refactoring, removed PhysicsInterface, cleaned up demos to make use of btDynamicsWorld derived classes.

removed two cached optimizations, type in btTransform and cached inverse transform (todo: test performance impact)
committed fixes that make the code adhere to 'who creates it, also destroys it'

Demos/BspDemo/BspDemo.h

@@ -22,6 +22,8 @@ class BspDemo : public DemoApplication
 {
 	public:
 
+	virtual ~BspDemo();
+
 	void	initPhysics(char* bspfilename);
 
 	virtual void clientMoveAndDisplay();