[PATCH] cli/new: document new exit code

[Jani Nikula]

On Sat, 26 Nov 2016, David Bremner <david at tethera.net> wrote:
> It seems important to give the numeric return code for people writing
> scripts. Hopefully deviations from this convention are rare.

*blush*

As a token of my gratitude, a test for the change follows. I'm not sure
if it's quite ready for merging, but the ground work is there.

Thanks,
Jani.