Check alerts when session changes, from Patrick Palka.

cmd-switch-client.c

@@ -131,6 +131,7 @@ cmd_switch_client_exec(struct cmd *self, struct cmd_q *cmdq)
 	server_check_unattached();
 	server_redraw_client(c);
 	s->curw->flags &= ~WINLINK_ALERTFLAGS;
+	alerts_check_session(s);
 
 	return (CMD_RETURN_NORMAL);
 }

server-fn.c

@@ -389,6 +389,7 @@ server_destroy_session(struct session *s)
 			session_update_activity(s_new, NULL);
 			gettimeofday(&s_new->last_attached_time, NULL);
 			server_redraw_client(c);
+			alerts_check_session(s_new);
 		}
 	}
 	recalculate_sizes();