bug#25611: 26.0.50; dired-do-compress unpacks .tgz files

[Glenn Morris]

Comments from rms:

http://lists.gnu.org/r/emacs-devel/2018-11/msg00268.html

    It does not literally make sense to "decompress" an archive.  Any kind
    of archive.  That stretches the meaning of "decompress".

    Such stretching might be ok, if it led to no confusion or conflict.
    However, what we see is that it does lead to confusion.  So Z should
    not unpack archives -- not even zip archives.

    Instead, we should have a different letter for unpacking archives.
    I suggest moving dired-do-find-regexp to F
    ad defining A to unpacking an archive.