bug#22457: 24.5; [PATCH] `dired-mark-if' should not count non-changes

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

> Oh, btw, this patch line
> 
>   (looking-at-p (char-to-string dired-marker-char))
> 
> is not good if dired-marker-char is a regexp special like . or ?, I
> guess (regexp-quote missing)?

It's a good point; it would be clearer to wrap the
arg to `looking-at-p' with `regexp-quote'.

It works as coded, however, because Emacs regexp
matching treats a special char such as `*' as
non-special in such a context.

I'm not saying it's good to rely on that (documented)
behavior - it's better to use `regexp-quote'.

See (elisp)`Syntax of Regexps':

  *Please note:* For historical compatibility, special characters are
  treated as ordinary ones if they are in contexts where their special
  meanings make no sense.  For example, '*foo' treats '*' as ordinary
  since there is no preceding expression on which the '*' can act.  It is
  poor practice to depend on this behavior; quote the special character
  anyway, regardless of where it appears.