bug#26892: 25.2; whitespace-mode does not turn off correctly

[Nick Helm]

> A couple of notes, for the future:
>
>  . The test at first failed for me, and needed some tweaking, because
>    whitespace-mode refuses to turn on in batch mode.  I guess you ran
>    the tests in interactive mode?  You should run tests in batch.

Sorry, yes, I did. I read about batch testing in the manual, but didn't
click that most tests need to run that way. Of course they do, now that
I think about it. 

>  . The patch was not applicable without manual editing, because it
>    used file names like whitespace-a.el, which don't exist.  Please in
>    the future submit patches produced against the correct file names,
>    preferably with "git diff" or somesuch.
>
>  . Please include with the patch a ChangeLog-style commit log message
>    (see CONTRIBUTE for details).
>
>  . Finally, this contribution exhausts the amount of changes we can
>    accept from you without legal paperwork, so I encourage you to
>    start the paperwork rolling, for us to be able to accept your
>    future contributions.  (I can send you the forms off-list if you
>    want.)

I'd like to keep contributing where I can, so please do send the
paperwork when you have a moment. 

Thank you for the feedback and for fixing up the code. It is very much
appreciated!