bug#36828: 27.0.50; Uninstalled emacs shows installed documentation

[Eli Zaretskii]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Cc: stepnem@gmail.com,  36828@debbugs.gnu.org
> Date: Mon, 28 Oct 2019 21:21:21 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Checking for the presence of the "Makefile" file using the same method
> >> we use for "NEWS".
> >
> > Presence where?
> 
> In installation-directory (provided that it is not nil).
> 
> > Anyway, Makefile is too common a file, I think we should look for
> > something more specific to Emacs.
> 
> We have plenty to choose (lib-src/emacsclient, for instance) but IMO if
> Makefile exists in installation-directory that's a sure sign.

If it is not nil, and the test of equality between srcdir and
invocation-directory fails, then you already know that you are running
uninstalled, but outside of the src directory.  Right?  Then you don't
need looking for Makefile or anything else, right?