SGN mod for modlnp to fix Rtnmin


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/optimizer@874 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added test fn


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/optimizer@875 edb9625f-4e0d-4859-8d74-9fd3b1da38cb