[Rd] RFC: allow packages to advertise vignettes on Windows

[Duncan Murdoch]

I think we've agreed about adding an option to the vignette() function 
to allow the user to choose to see all vignettes in installed packages, 
or only those that are attached.  Adding this is pretty trivial, and 
I'll put it into R-devel soon.

I'd like to set the default to show only attached packages, which would 
be consistent with the behaviour of demo() and data().  Vignettes are 
still less common than demos or data, so if I do this, I'll also change 
the "none found" message to something like

 > vignette()
no vignettes found

Use 'vignette(all = TRUE)'
to list the vignettes in all *available* packages.

Will this change to the default behaviour cause a lot of trouble for anyone?

Duncan Murdoch