minor fix to coefplot.mlm

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/heplots@175 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
import(car) to avoid CRAN nag

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/heplots@176 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
git-svn-id: svn://svn.r-forge.r-project.org/svnroot/heplots@177 edb9625f-4e0d-4859-8d74-9fd3b1da38cb