[Rd] vignettes with similar names

[Michael Sumner]

In R 3.0.2 Patched (2014-01-31 r64905) and 3.0.3 beta (2014-02-25
r65077) I see a problem loading vignettes when I create a package with
two vignettes with similar names, e.g.

"vignette3"
"vignette3-install"

These seem not to be distinguished, and I get this

vignette("vignette3")
vignette ‘vignette3’ not found

vignette("vignette3-install")
Warning message:
vignette ‘vignette3-install’ found more than once,
using the one found in ‘.’

This was not an issue in 2.15.3, and it works correctly in R-dev
(2014-02-17 r65021).

Cheers, Mike.