bug#49786: 28.0.50; [PATCH] package-install shouldn't change default-directory

[Eli Zaretskii <eliz@gnu.org>]

> From: dick <dick.r.chiang@gmail.com>
> Date: Fri, 30 Jul 2021 15:12:06 -0400
> 
> Commit 606b783acb leverages a 2015 hack that extracts the
> package version from the buffer file name, only he has to
> explicitly `set-visited-file-name` to do it.
> 
> `set-visited-file-name` has the adverse side effect of
> changing the default-directory, and that causes me problems.

Ioannis, could you please tell why you needed to call
set-visited-file-name there?

> If the ostensible reason for bug#48137 was to get the "lm"
> functions dos-aware, then why not do that instead of applying
> a workaround on top of a hack?

This was discussed in that bug, and the conclusion was that it's a
worse alternative than the solution eventually installed.

> * test/lisp/emacs-lisp/package-tests.el (package-test-install-file-EOLs):
> What is "mac" encoding?  It doesn't work.  The names of
> salient coding systems do not coincide with the predominant
> desktop operating systems.

The 'mac' encoding is documented in the ELisp manual.  Please don't
remove its testing here.