bug#34489: 25.2; pdb fails if directory contains '++'

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Fri, 5 Jul 2019 17:51:00 +0200
> Cc: a.soroa@ehu.eus, 34489@debbugs.gnu.org
> 
> > I think both [:print:] and .* would be too radical, as I'm not sure
> > including control characters and arbitrary whitespace will not break
> > something.  But maybe [:graph:] is better than [:alnum:].
> >
> > In any case, I think we want a comment there saying that this is to
> > allow more characters in file names shown in the prompt.
> 
> How about the attached patch?

Thanks, pushed to the master branch.