Merge branch 'lt/gpg-show-long-key-in-signature-verification-maint' into lt/gpg-show-long-key-in-signature-verification

Linus's original was rebased to apply to the maintenance track just
in case binary distributors that are stuck in the past want to take
it to their older codebase.  Let's merge it up to more modern
codebase that has Peff's gpg-interface clean-up topic that appeared
after Git 2.9 was tagged.

* lt/gpg-show-long-key-in-signature-verification-maint:
  gpg-interface: prefer "long" key format output when verifying pgp signatures