allow placing a copy of Sweave.sty in the vignette directory
cnt: don't refer too much to TeXlive 2007, it's 2013 now
fix: use IfFileExists for xelatexEx.pdf to allow testing compilation
Revert "fix: use IfFileExists for xelatexEx.pdf to allow testing compilation"

This reverts commit 3bedc1e2c730be08a950c8be80c75118db9051b2.