Instead of having tag -v fork to run verify-tag, use the
gpg_verify_tag() function directly.
Helped-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Santiago Torres <santiago@nyu.edu> Reviewed-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>