if ess-swv-pdflatex-commands is of length 1 don't ask

git-svn-id: https://svn.r-project.org/ESS/trunk@5375 0bbaf3bd-34e0-0310-bf65-c717079852d4
don't append --unique to okular (consistent with other viewers)

git-svn-id: https://svn.r-project.org/ESS/trunk@5376 0bbaf3bd-34e0-0310-bf65-c717079852d4
add a CHOOSE argument to ess-swv-weave to interactively choose between available weavers (sweave and knitr)

git-svn-id: https://svn.r-project.org/ESS/trunk@5377 0bbaf3bd-34e0-0310-bf65-c717079852d4