Merge branch 'hi/gpg-use-check-signature'

"git merge signed-tag" while lacking the public key started to say
"No signature", which was utterly wrong.  This regression has been
reverted.

* hi/gpg-use-check-signature:
  Revert "gpg-interface: prefer check_signature() for GPG verification"

diff --cc builtin/fmt-merge-msg.c
Simple merge

diff --cc gpg-interface.c
Simple merge

diff --cc gpg-interface.h
Simple merge

diff --cc log-tree.c
Simple merge