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

[Drew Adams]

> Using lambdas should be ok most of the time.  But there's a certain
> risk
> of unintentionally having two copies of a function in a hook when the
> code is executed multiple times, e.g. if you load your init file twice,
> once compiled, and once the lisp source, because `add-hook' then can't
> know that it's the same function.  Most of the time even this has no
> visible effect, but when it has, it can be surprising and finding the
> cause can be hard, so I try to just avoid adding lambdas to hooks in my
> init file.

Also, if you're testing stuff and you add a lambda
form to a hook, and later you want to remove it,
you need to use exactly the same text - same
whitespace, everything.  The lambda form is taken,
in effect, as text, and it looks for an exact
textual match.

It's very good to get in the habit of not using
lambdas on hooks.