NEWS: added relevant changes that have already been implemented but that were not mentioned in the NEWS file

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1531 d36ae590-6c38-44c5-9ba5-7217e93607d8
added tests of the (default) nObs() method applied to selection models (both estimated by the 2-step procedure and estimated by ML)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1532 d36ae590-6c38-44c5-9ba5-7217e93607d8
added nObs() method for "selection" objects (currently identically to nObs.default() but this might change in the future

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1533 d36ae590-6c38-44c5-9ba5-7217e93607d8
added logLik() method for selection models (this method currently only works for models estimated by maximum likelihood (ML) but it does not work for models estimated by the 2-step method)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1534 d36ae590-6c38-44c5-9ba5-7217e93607d8
added tests of the logLik() method for selection models

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1535 d36ae590-6c38-44c5-9ba5-7217e93607d8