r23410: Merge the core of the cluster code.

r23410: Merge the core of the cluster code.

I'm 100% certain I've forgotten to merge something, but the main code
should be in. It's mainly in dbwrap_ctdb.c, ctdbd_conn.c and
messages_ctdbd.c.

There should be no changes to the non-cluster case, it does survive make
test on my laptop.

It survives some very basic tests with ctdbd enables, I did not do the
full test suite for clusters yet.

Phew...

Volker
(This used to be commit 15553d6327a3aecdd2b0b94a3656d04bf4106323)