[PATCH 3 of 3] hook: report untrusted hooks as failure (issue5110) (BC)

[timeless]

Pierre-Yves David wrote:
> timeless wrote:
>> can i convince you to replace "denied" with "skipped"?

> Skipped seemed a bit too light for the abort case:
>
> Abort: pretxnopen.foo hook skipped (from unstrusted source)
>
> (it is not really "skipped" as it aborted the whole operation).
>
> What do you think?

I'm thinking "Can I get it in a sentence?"
But in practical terms, can you add tests w/ this commit showing
pretxnopen/pretxnclose (passing, failing)?

"forbidden" is probably the right word in the pretxnopen case (instead
of denied).