More diagnostics about partial rule matches in failure logs

[dbarnett]

For emails that fail to match any rule, it would be wonderful if the failure report could list any diagnostics about rules they partially matched. For instance, given a rule like:

(and
  (from someone@example.com)
  (receiver someoneelse@example.net))

You might get a failure email with an error like:

Process email failed: Thread "Invitation to the party" has no action, does it match any rule?
Didn't match rule "(and (from someone@…" on row 5 because sender was "someone@example.net", not "someone@example.com".

[ranmocy]

That sounds useful.

Just a reminder that you are the contributor so you could write and push. If you'd like to some input on the change, then create a pull request and we could discuss.