Log Message:
Take steps toward running under other UCSPI-TLS server implementations:

- Set CADIR in the environment.

- Prefer a separate keyfile for TLS. If it's not present, attempt to
  generate it by copying out the private key from the certfile.

- Don't provide an affordance for overriding the compiled-in cipherlist.

- Be willing to enable TLS without a DH params file.

While here, invent control/localfilters. If it exists, it's a sequence
of filters for SMTP connections on localhost.

Bump version.