add btActivationCollisionAlgoritm to fix deactivation problems, reported here:

http://bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=2616

provide access to active objects, requested here:
http://code.google.com/p/bullet/issues/detail?id=128

src/BulletDynamics/Dynamics/btDiscreteDynamicsWorld.h

@@ -42,7 +42,6 @@ protected:
 
 	btAlignedObjectArray<btTypedConstraint*> m_constraints;
 
-
 	btVector3	m_gravity;
 
 	//for variable timesteps
@@ -79,6 +78,7 @@ protected:
 
 	void	debugDrawSphere(btScalar radius, const btTransform& transform, const btVector3& color);
 
+
 public:
 
 
@@ -90,6 +90,7 @@ public:
 	///if maxSubSteps > 0, it will interpolate motion between fixedTimeStep's
 	virtual int	stepSimulation( btScalar timeStep,int maxSubSteps=1, btScalar fixedTimeStep=btScalar(1.)/btScalar(60.));
 
+	
 
 	void	addConstraint(btTypedConstraint* constraint, bool disableCollisionsBetweenLinkedBodies=false);
 
@@ -114,7 +115,6 @@ public:
 		return this;
 	}
 
-
 	virtual void	setGravity(const btVector3& gravity);
 	virtual btVector3 getGravity () const;