unix socket: protocol v0.2

unix socket: protocol v0.2

This patch updates the unix socket protocol. Messages send from
the server and the client have now a '\n' at the end. This allows
both sides to detect easily the end of a command.

As a side effect, this fixes the problem of long answer in
suricatasc. There is now a limit at the arbitrary value of 65536.

Backward compatility is preserved as a client with the older
version of the protocol can still connect to a Suricata with
version 2 of the protocol.