update  all KL methods

@karlnapf 
I send all the changes at one shot to see if it work or not.
Let me know your suggestion so that I can send PRs separately for KL methods.
I think you do double computation here.
isPositive already has to look at the Eigenvalues of the matrix, so it computes a factorization. This could be in fact used to compute the log-determinant, but you are calling another method there.
Sorry for not having spotted this earlier, but now with the loop it became more apparent.

Do you see what I mean? I think you should just compute the log-det from the m_ldlt class directly. Or not check it this way.