Moved some variables to static ones
Only leader process serves the clients and only over tcp

UNIX socket support has been dropped, now only a tcp client socket is
working. Client now always gets redirected to leader process.
Rudimentary support for this has been implemented in the strings client.

Also mersenne now informs the client about cluster membership, so that
the client knows where to reconnect in case of leader failure.
Implicit increase of ballot number upon reject