[Rd] build packages with vignettes in Windows

[Michael]

On 29 Apr 2008, Duncan Murdoch wrote:
 
> Right, you don't need to set the system path for everything, but you do
> need to set it in CMD (or other shell) before running Rcmd.

For Win 2K/XP/Vista, the system path can be set (through the GUI interface,
not sure how to do it with scripts) without restarting, for new CMD
processes started afterwards.

Michael