Internal function to suppress an annoying warnings from chol()
matrixnotposdef.handler(w)a warning
not a warning if the warning was "matrix not positive definite" or "the matrix is either rank-deficient or indefinite"
See: https://stat.ethz.ch/pipermail/r-help/2012-February/302407.html See: http://romainfrancois.blog.free.fr/index.php?post/2009/05/20/Disable-specific-warnings