bug#38818: Dired: mention deleting buffers, not just windows

[Drew Adams]

> But I see the annoyance of tons of unneeded dired buffers lying around,
> too.

`C-x C-v' prevents that.

---

Also, with Dired+ you can use `C-M-R' to toggle
reusing Dired buffers (instead of accumulating
them).  `RET' and `^' then automatically do what
`C-x C-v': replace the previous Dired buffer
with the new one.

It's a toggle because you can easily want to
sometimes keep Dired buffers by default and
sometimes want to replace them by default,
depending on what you're doing.

When keeping by default you can always use
`C-x C-v' to replace occasionally.