new function zitest(), currently quite primitive

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/countreg@80 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
new function zitest(), currently quite primitive

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/countreg@81 edb9625f-4e0d-4859-8d74-9fd3b1da38cb