bug#38189: 27.0.50; dired-aux fails to load format-spec, leading to runtime error in dired-do-compress-to

[Štěpán Němec]

On current master, but released Emacs 26.3 has the same problem:

Recipe:
-------
emacs -Q
C-x d [or otherwise invoke dired]
[pick a file]
M-x dired-do-compress-to [and provide suitable value to the prompt]

=> Symbol’s function definition is void: format-spec
-------

`dired-do-compress-to' uses the function `format-spec', provided by
format-spec.el, but its containing library (dired-aux.el) only declares
the function without providing for loading it when needed.

In GNU Emacs 27.0.50 (build 15, x86_64-pc-linux-gnu, X toolkit, Xaw scroll bars)
 of 2019-11-12 built on panda
Repository revision: ececf739cea15d763d7fe99b92d618039071c728
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12005000
System Description: Arch Linux

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Štěpán