* Added cs_addr field to struct CitContext -- holds a dotted quad string

* Added cs_addr field to struct CitContext -- holds a dotted quad string
  of the user's source IP (if applicable).  It's big enough to hold other
  types of address strings in the future (such as IPv6).
* locate_host() populates cs_addr when on a network connection.
* serv_smtp.c now saves the IP address in the proper place in
  the Received: header.
* is_public_client() no longer accepts a hostname.  It just looks at
  CC->cs_host instead.