linearPredictors.probit() now returns a vector rather than a one-column matrix

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1521 d36ae590-6c38-44c5-9ba5-7217e93607d8
added references to model.frame.binaryChoice() and model.matrix.binaryChoice() to the documenation of several methods for "probit" models (probit-methods.Rd)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1522 d36ae590-6c38-44c5-9ba5-7217e93607d8
added tests for model.frame.binaryChoice() and model.matrix.binaryChoice()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1523 d36ae590-6c38-44c5-9ba5-7217e93607d8
added "links" between the documentation files for the methods for binaryChoice / probit models; a few other improvements in these docuentation files

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1524 d36ae590-6c38-44c5-9ba5-7217e93607d8
NEWS: mentioned improvement of the documentation

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1525 d36ae590-6c38-44c5-9ba5-7217e93607d8