Allow Q to be passed to pmatrix.(piecewise.)msm instead of a model


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/msm@63 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
update changelog


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/msm@64 edb9625f-4e0d-4859-8d74-9fd3b1da38cb