warnings now also propagated nicely in print.mixed when type = 2.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@104 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added tests via testthat package

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@105 edb9625f-4e0d-4859-8d74-9fd3b1da38cb