This patch also combines ipv4-dns and ipv6-dns options
that are now handled as aliases to dns.
A side-effect of this patch is that the local keyword is no
longer supported.
This change puts a proc_st that its client has terminated to a "zombie"
state. That state will allow a client that connects later using the
same TLS session ID to reclaim it. That way clients that try to authenticate
by sending their credentials in different sessions can still authenticate with
ocserv. That however puts more trust to worker processes (as the main
process has no way of telling whether a TLS session is certainly
resumed).
