Iterate only over non-static rigid bodies, instead of all collision objects

http://bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=18&t=3625
http://code.google.com/p/bullet/issues/detail?id=128

Attempt to fix issue in mesh striding, multiple-mesh-parts were broken.

src/BulletDynamics/Dynamics/btDiscreteDynamicsWorld.h

@@ -42,6 +42,8 @@ protected:
 
 	btAlignedObjectArray<btTypedConstraint*> m_constraints;
 
+	btAlignedObjectArray<btRigidBody*> m_nonStaticRigidBodies;
+
 	btVector3	m_gravity;
 
 	//for variable timesteps