bug#18716: Patch for this bug

[Eli Zaretskii]

> From: Reuben Thomas <rrt@sc3d.org>
> Date: Mon, 28 Nov 2016 21:32:03 +0000
> Cc: Eli Zaretskii <eliz@gnu.org>, 18716@debbugs.gnu.org
> 
> ​Thanks for the heads up, that's great news! It bothered me that there was no 
> easy way to do this previously.
> 
> ​I updated my patch so that dired-omit-case-fold is now a three-valued 
> variable which defaults to 'filesystem,
> and a helper function that checks (filename-case-sensitive-p dired-directory) 
> when this value is used.
> 
> I've added info and NEWS documentation for dired-omit-case-fold.

Thanks, a few comments below.  With those fixed, please push to
master.

> +@vindex dired-omit-case-fold
> +@item dired-omit-case-fold
> +
> +Default:  @code{filesystem}

Please mention this value in the text that follows.

> +                                                           Set to
> +@code{nil} to be always case-sensitive, and @code{t} to be always
> +case-sensitive.

So which is it? ;-)

>  +++
> +** The new user variable 'dired-omit-case-fold' allows the
> +case-sensitivity of dired-omit-mode to be configured.  It defaults to
                                             ^^^^^^^^^^
Our terminology is "customized".

Bonus points for avoiding passive tense altogether ("... allows
customization of case-sensitivity ...").

> +(defcustom dired-omit-case-fold 'filesystem
> +  "Whether `dired-omit-mode' will use case-folding to match the
> +regexp of files to omit.  When nil, always be case-sensitive; when

The first line of a doc string should be a complete sentence.

> +(defun dired-omit-case-fold-p (dir)
> +  "Return t if, according to `dired-omit-case-fold',
> +  `dired-omit-mode' should use case folding to interpret its
> +  regexp in directory DIR."

Likewise.