vc-cvs-stay-local vs vc-stay-local

[Jason Rumney]

While trying to help a user who was disturbed by the CVS backup files
that Emacs now creates, I came across vc-stay-local. After advising
him to set that to nil, it did not appear to do anything. Apparently
he needs to set vc-cvs-stay-local instead, but there is no mention of
that in the doc string for vc-stay-local, in fact both doc strings are
exactly the same. After starting emacs -Q, vc-stay-local is listed as
a completion for C-h v vc- but vc-cvs-stay-local is not.

Do we need both these variables? If so, the way they interact with
each other is not at all clear, so the doc strings need some work.