Better DEBUG error message when num of arguments is wrong.

src/debug.c

@@ -338,7 +338,7 @@ void debugCommand(redisClient *c) {
         server.active_expire_enabled = atoi(c->argv[2]->ptr);
         addReply(c,shared.ok);
     } else {
-        addReplyErrorFormat(c, "Unknown DEBUG subcommand '%s'",
+        addReplyErrorFormat(c, "Unknown DEBUG subcommand or wrong number of arguments for '%s'",
             (char*)c->argv[1]->ptr);
     }
 }