Add client code to detect attempts to connect to 127.0.0.1 etc

We detect and reject said attempts if there is no chosen exit node or
circuit: connecting to a private addr via a randomly chosen exit node
will usually fail (if all exits reject private addresses), is always
ill-defined (you're not asking for any particular host or service),
and usually an error (you've configured all requests to go over Tor
when you really wanted to configure all _remote_ requests to go over
Tor).

This can also help detect forwarding loop requests.

Found as part of bug2279.

src/or/connection.c

@@ -1205,9 +1205,11 @@ connection_init_accepted_conn(connection_t *conn, uint8_t listener_type)
           conn->state = AP_CONN_STATE_SOCKS_WAIT;
           break;
         case CONN_TYPE_AP_TRANS_LISTENER:
+          TO_EDGE_CONN(conn)->is_transparent_ap = 1;
           conn->state = AP_CONN_STATE_CIRCUIT_WAIT;
           return connection_ap_process_transparent(TO_EDGE_CONN(conn));
         case CONN_TYPE_AP_NATD_LISTENER:
+          TO_EDGE_CONN(conn)->is_transparent_ap = 1;
           conn->state = AP_CONN_STATE_NATD_WAIT;
           break;
       }