Log Message:
security/signify: update to 0.12.

The version number is kept consistent with that of outils.
Sources have been synced with upstream OpenBSD/src.

Changes relevant to signify:

- Unused variables moved under !VERIFYONLY
- In -C mode, the public key is optional since it can be deduced from
the untrusted comment.  In this case, don't ignore -t but rather make
it work as expected.