[Samba] how to build samba with ctdb support

[steve]

We have unpacked samba.4.1.11.
./configure options we see are:

  --with-cluster-support
            Build with cluster-support support (default=auto)
   --with-ctdb-dir=CTDB_DIR
            Directory under which ctdb is installed
 --without-ad-dc
  --enable-old-ctdb
            enable building against (too) old version of ctdb
(default=false)

1. What does '(default=auto)' mean?
2. How do I force it to build with cluster support?
3. Which ctdb directory does it want? The the tarball has left stuff
at:  /usr/local/sbin, /usr/local/bin, /usr/local/etc/ctdb, /usr/local/var/lib/ctdb, /var/ctdb, /var/lib/ctdb and /var/lib/lib/ctdb
4. Any other options we need for ctdb?

Thanks,
Steve