/* Construct a new MIME node pointing to the root message part of
* message. If crypto->verify is true, signed child parts will be
* verified. If crypto->decrypt is NOTMUCH_DECRYPT_TRUE, encrypted
/* Construct a new MIME node pointing to the root message part of
* message. If crypto->verify is true, signed child parts will be
* verified. If crypto->decrypt is NOTMUCH_DECRYPT_TRUE, encrypted