Server: Make persistent state directory mode u=rwx,go=
The Makefile target "install-server" creates the server persistent state directory /var/lib/mandos as mode u=rwx,go= (0700). Make this also the case for the Debian package (unless overridden by dpkg-statoverride).
* debian/mandos.postinst (configure): Fix state directory permissions, but only if not listed by "dpkg-statoverride".