bug#33757: 27.0.50; dired-du-mode displays incorrect human readable file sizes for non-GNU systems

[Matthew Newton]

* Reproduction
1. Run MacOS (Or I suspect any OS that is not GNU-based).
2. emacs -Q
3. M-x package-install RET dired-du RET
4. M-x dired RET ~ RET
5. M-x dired-du-mode RET
6. Notice that file sizes are displayed in kbytes, not bytes (they are 
displayed in bytes in a GNU-based system)
7. M-x dired-du--toggle-human-readable RET
8. M-x z z (to enable file sizes displated in human readable form, i.e. sizes 
ending in k, M, G, T)
9. File sizes displayed are one order of magnitude smaller than their actual 
size (e.g. if the file size is 2MB then it will be displayed as 2kB)

* Discussion
The problem seems to arise when the custom variable dired-du-used-space-program 
is set. For a GNU-based system, it gets set to "du -sb" but for MacOS it gets 
set to "du -sk". Then later when the human readable sizes are calculated, this 
difference does not appear to be accounted for.

Why do we make the distinction between a GNU-based system and anything else? 
Can we just change the logic setting dired-du-used-space-program to always run 
"du -sb”?


Cheers,
Matt

P.S. This is my first Emacs bug report so please help me out if I should report 
it differently.