strip some trailing whitespace

This is in my .emacs:

;;;
;;; delete trailing white space
;;;
(add-hook 'before-save-hook 'delete-trailing-whitespace)
;;;
added two usepackage lines for threeparttable and tabulary

my LaTeX/Org installation wouldn't process the file to PDF without
these two lines:
   #+LATEX_HEADER: \usepackage{threeparttable}
   #+LATEX_HEADER: \usepackage{tabulary}
added a backslash before the dollar sign in $USER

LaTeX seemed to want this, but i thought that was weird, since usually
org mode does a nice job with this.