We accidentally haven't been using $TMUX to work out the session for a

while and in fact it is less useful that using the client ttyname. So
don't bother and don't pass it from the client. If we need it in future
it is in c->environ.

server-client.c

@@ -62,6 +62,8 @@ server_client_create(int fd)
 		fatal("gettimeofday failed");
 	memcpy(&c->activity_time, &c->creation_time, sizeof c->activity_time);
 
+	environ_init(&c->environ);
+
 	c->cmdq = cmdq_new(c);
 	c->cmdq->client_exit = 1;