[j-nsp] Config archive subtleties

[Phil Shafer]

Phil Mayers writes:
>Agreed; preserving the separate commits and metadata is a big win, IMO, 
>and I really like the feature. It was surprising and disappointing to 
>find it had hung up!

Apologies for that.  Failures should be loud, and should be a formal
event, so you can use an event policy to attach custom behavior to
this failure.

I've added this (and David's and ytti's requests) to PR 910647.

Thanks,
 Phil