Merge branch 'st/verify-tag'

Merge branch 'st/verify-tag'

Unify internal logic between "git tag -v" and "git verify-tag"
commands by making one directly call into the other.

* st/verify-tag:
  tag -v: verify directly rather than exec-ing verify-tag
  verify-tag: move tag verification code to tag.c
  verify-tag: prepare verify_tag for libification
  verify-tag: update variable name and type
  t7030: test verifying multiple tags
  builtin/verify-tag.c: ignore SIGPIPE in gpg-interface