added tests for many methods applied to fitted binary outcome selection models

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1545 d36ae590-6c38-44c5-9ba5-7217e93607d8
added tests for stdEr() and lrtest() applied to selection models

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1546 d36ae590-6c38-44c5-9ba5-7217e93607d8
added a help page for documenting several methods for selection objects; updated the "seealso" sections of many help pages for selection models and methods

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1547 d36ae590-6c38-44c5-9ba5-7217e93607d8