fixed bug in residuals.selection( , part = "selection" ) that occured when the dependent variable of the selection model was a factor

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1564 d36ae590-6c38-44c5-9ba5-7217e93607d8
corrected a typo in the test script

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sampleselection@1565 d36ae590-6c38-44c5-9ba5-7217e93607d8