faster dmvnorm by Matteo Fasiolo

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/mvtnorm@261 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
start 0.9-9998

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/mvtnorm@262 edb9625f-4e0d-4859-8d74-9fd3b1da38cb