[ESS] Bug in ess-swv-PDF on Windows

[Kevin Wright]

ess-swv-PDF fails on Windows because it tries to launch a bash shell
in order to open a pdf reader.

Replacing this line:
(shell-command (concat pdfviewer " " namestem ".pdf &")))

with
(w32-shell-execute "open" (concat namestem ".pdf") nil 1))

fixes the problem for me.

Obviously there needs to be some kind of (if-i-am-running-mswindows ()
()) check here too.

Sincerely,

Kevin Wright