Output updated_covariance from smoother

more on 55191758, I have a question:

• we are issuing in oo_.Smoother.Variance the one step ahead variance of variables V(t+1|t). this is in principle a duplicate of the FilteredVariablesKStepAheadVariances, for k=1.
• we are issuing in oo_.Smoother.State_uncertainty the smoother covariances V(t|T)
• we are not issuing the updated covariances V(t|t): should we also provide this?

V(t|t) would be available already from matlab/missing_DiffuseKalmanSmootherH3_Z.m (P variable), while for matlab/missing_DiffuseKalmanSmootherH1_Z.m it is not (should be computed on purpose).