bug#41868: [PATCH] Add project-clean-up command

[Juri Linkov]

> On 16.06.2020 20:12, Philip K. wrote:
>> It sounds good, so I used it in the revised patch below, together with a
>> few other minor improvments which Basil mentioned.
>
> Thank you, I pushed with some minor changes.
>
> - Docstring further rephrased based on Basil's suggestion.

Why none of recent changes were mentioned in etc/NEWS?

> - The variable renamed to project-kill-buffers-skip-conditions, hope you
>   don't mind.

But we already agreed on a shorter name project-kill-buffers-ignore,
and Philip sent the patch that renames it.