[Rd] [ENH] Clarify rsync flavors (PR#2886)

[Douglas Bates]

ross at biostat.ucsf.edu writes:

> The 1.7.0 (2003-04-16) "R Installation and Adminsistration"
> manual mentions various flavors of R available from rsync (section
> 1.2, p. 1).  These are also referred to in various other sources on
> and offline (e.g., the FAQ).
> 
> The meaning of r-release vs r-patched was not entirely clear to me.
> How is the patched version patched?  Should it just have bug fixes,
> and so likely be more reliable than r-release?  Or is it patched with
> a lot of development changes, so that it's quite like r-devel?

R-patched = original sources plus bug-fix patches
R-devel = development sources that include bug-fix patches _and_ new capabilities

We had rather hoped that our choice of names would make this
distinction clear.