Update Dovecot Sieve plugin to 1.0.3.

- Improved vacation reply checks, log discarded vacation replies
- Expand ~ to home directory in sieve path
- If compiled script has the exact same mtime as the source script, assume the
  script hasn't changed (changed "<" check to "<=").
- Unfold multiline headers before comparing them.
- Improved error logging.

(ghen)