add new Al-Mohy-Higham(2009) "AlMoHi09" method 
from Drew Schmidt -- inspite of bug/thinko/typo matexp_scale_factor()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/expm@80 edb9625f-4e0d-4859-8d74-9fd3b1da38cb