Completed rstree/pctree CITATION and fixed minor things in other CITATIONS.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/prefmod@202 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added iterlim and hessian argument to RaschModel()/raschtree() to be consistent with RSModel()/rstree() and PCModel()/pctree()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/prefmod@203 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Call modeltools:::ParseFormula() directly.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/prefmod@204 edb9625f-4e0d-4859-8d74-9fd3b1da38cb