Re: master 6d6bf46 2/2: Make dired-do-compress work for *.tar.gz files

[Eli Zaretskii <eliz@gnu.org>]

> From: Achim Gratz <Stromeko@nexgo.de>
> Date: Wed, 14 Oct 2015 20:51:19 +0200
> 
> > For .tar.bz2, uncompress with bunzip2 to get .tar, for .tar.xz,
> > uncompress with unxz to get .tar.  Is that what you wanted?
> 
> This is what a reasonably recent GNU tar offers:

GNU Tar needs the programs I mentioned anyway, so if GNU Tar can
handle those archives, an explicit pipe with those programs will also
work.

By contrast, detecting GNU Tar and then providing an alternative for
non-GNU Tar versions will IMO make the code much more complex, for no
good reason.

And, as long as we are talking about this, I'd suggest to add support
for libarchive's bsdtar, which can unpack all those formats (and many
more) without any external programs.  Adding that support boils down
to checking if bsdtar is available.