Switch some Conf settings over to being bool.

I think this is the full set of things that ought logically to be
boolean.

One annoyance is that quite a few radio-button controls in config.c
address Conf fields that are now bool rather than int, which means
that the shared handler function can't just access them all with
conf_{get,set}_int. Rather than back out the rigorous separation of
int and bool in conf.c itself, I've just added a similar alternative
handler function for the bool-typed ones.

ssh1connection.c

@@ -663,7 +663,7 @@ static int ssh1_agent_forwarding_permitted(ConnectionLayer *cl)
 {
     struct ssh1_connection_state *s =
         container_of(cl, struct ssh1_connection_state, cl);
-    return conf_get_int(s->conf, CONF_agentfwd) && agent_exists();
+    return conf_get_bool(s->conf, CONF_agentfwd) && agent_exists();
 }
 
 static void ssh1_connection_special_cmd(PacketProtocolLayer *ppl,