bug#29323: kill-do-not-save-duplicate, FR

[Drew Adams <drew.adams@oracle.com>]

> Currently variable kill-do-not-save-duplicates checks only the (car kill-ring) as docu explains: 
>
> Do not add a new string to ‘kill-ring’ if it duplicates the last one.
> The comparison is done using ‘equal-including-properties’.
> AFAIU it would be trivial replace this check by a call of "member",
> thus checking > the whole kill-ring.

Why do that?  Why not just prevent duplicates in the first place,
which is what the option currently does?

If you for some reason get duplicate entries somehow, in spite of
using the option to prevent them, you can always remove them.

I don't understand how that would be something that would happen
normally.  What is the problem that this would try to solve/prevent?

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