* mml2015.el: Require mml-sec instead of password.

* mml2015.el: Require mml-sec instead of password.
(mml2015-verbose): Inherit the default value from mml-secure-verbose.
(mml2015-cache-passphrase): Inherit the default value from
mml-secure-cache-passphrase.
(mml2015-passphrase-cache-expiry): Inherit the default value from
mml-secure-passphrase-cache-expiry.

* mml1991.el: Require mml-sec instead of password.
(mml1991-verbose): Inherit the default value from mml-secure-verbose.
(mml1991-cache-passphrase): Inherit the default value from
mml-secure-cache-passphrase.
(mml1991-passphrase-cache-expiry): Inherit the default value from
mml-secure-passphrase-cache-expiry.

* mml-sec.el: Require password.
(mml-secure-verbose): New user option.
(mml-secure-cache-passphrase): New user option.
(mml-secure-passphrase-cache-expiry): New user option.