[Rd] getOption("repositories")

[Jeff Gentry]

> It isn't needed to be set any more by default: it merely duplicated the
> information in options CRAN and BIOC.

IMO, it is more useful then that, however.  The nice thing about
"repositories" is that it provided one spot which could have 1->n
repositories listed.  Having a catch all "repositories" option makes it
easier to add new repositories in the future (functions written to work
against online repositories only have to work against
'getOption("repositories")' and not worry about having to hardcode any
future repositories) as well as allowing the user to add in repositories
of their own on their person setup.

-J