Replace use of Sequoia's backend with a custom key store.

- Sequoia's key store doesn't meet pep's needs (in particular, the
ability to search on a key's user id) and trying to shoehorn pep's
needs onto Sequoia's key store abstractions is just introducing
overhead with no appreciable gain in functionality.

- This patch changes the Sequoia backend to use a local sqlite
database to store the public keys.

// This file is under GNU General Public License 3.0

// see LICENSE.txt

#include "email.h"

PEP_STATUS email_sendto(PEP_SESSION session, const message *msg)

{

    return PEP_STATUS_OK;

}

PEP_STATUS email_readnext(PEP_SESSION session, message **msg, PEP_transport_t **via)

{

    return PEP_STATUS_OK;

}