fix in box-box contact generation: choose better contact point location (along contact normal) when objects are swapped.

move debugDrawWorld to btCollisionWorld.
improved CollisionInterfaceDemo, show how to perform a closest point query for objects that are not in the collision world.
removed a bit of garbage from the debug drawer

src/BulletCollision/CollisionDispatch/btCollisionWorld.h

@@ -150,6 +150,12 @@ public:
 		return m_debugDrawer;
 	}
 
+	virtual void	debugDrawWorld();
+
+	virtual void debugDrawObject(const btTransform& worldTransform, const btCollisionShape* shape, const btVector3& color);
+
+	void	debugDrawSphere(btScalar radius, const btTransform& transform, const btVector3& color);
+
 
 	///LocalShapeInfo gives extra information for complex shapes
 	///Currently, only btTriangleMeshShape is available, so it just contains triangleIndex and subpart