cksum: add tests to verify the presence of "*" (and question about usability of cksum)

[Sylvestre Ledru]

Hello,

The attached patch checks for a code path that wasn't covered before 
(afaik).

As a side note, the various combinations of --tag / --untagged and 
--binary / --text is producing some unexpected results at time :)
Maybe that ship sailed 10 or 20 years ago but would it make sense to 
reject --tag & --untagged (and binary/text) passed together?

Thanks,
Sylvestre

0001-cksum-add-tests-to-verify-the-presence-of.patch
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