bug#18478: [Patch] Mention the return value of `clone-indirect-buffer'

[Drew Adams <drew.adams@oracle.com>]

> > FWIW, I don't put a lot of stock in checkdoc, personally. ;-)
> 
> Its recommendations shouldn't be heeded blindly, indeed, but the
> 80-columns limit is something that should really be obeyed
> whenever possible.

Agreed wrt respecting doc-string line-length conventions.

But 80 chars is the absolute limit.  Doc strings should really be 
quite a bit shorter than that.  `emacs-lisp-docstring-fill-column'
defaults to 65, for example.

The actual convention is this (from (elisp) `Documentation Tips'):

 Format the documentation string so that it fits in an Emacs window
 on an 80-column screen.  It is a good idea for most lines to be no
 wider than 60 characters.  The first line should not be wider than
            ^^^^^^^^^^^^^
 67 characters or it will look bad in the output of `apropos'.

 You can fill the text if that looks good.  Emacs Lisp mode fills
 documentation strings to the width specified by
 `emacs-lisp-docstring-fill-column'.  However, you can sometimes
 make a documentation string much more readable by adjusting its
 line breaks with care.  Use blank lines between sections if the
 documentation string is long.