* mml2015.el (mml2015-extract-cleartext-signature): New function.

* mml2015.el (mml2015-extract-cleartext-signature): New function.
(mml2015-mailcrypt-clear-verify): Use it.
(mml2015-gpg-clear-verify): Use it.
(mml2015-pgg-clear-verify): Use it.
(mml2015-epg-clear-verify): Replace the current part with the output
from GnuPG; don't extract the plaintext by itself.

* mm-uu.el (mm-uu-pgp-beginning-signature): Abolish.
(mm-uu-pgp-signed-extract-1): Bind coding-system-for-read when calling
mml2015-clear-verify-function; don't touch the armor headers or
dash-escaped text here.