MINOR: hlua_fcn: register queue class using hlua_register_metatable()

Most lua classes are registered by leveraging the
hlua_register_metatable() helper. Let's use that for the Queue class as
well for consitency.

include/haproxy/hlua-t.h

@@ -60,6 +60,7 @@
 #define CLASS_CERTCACHE    "CertCache"
 #define CLASS_PROXY_LIST   "ProxyList"
 #define CLASS_SERVER_LIST  "ServerList"
+#define CLASS_QUEUE        "Queue"
 
 struct stream;
 

src/hlua_fcn.c

@@ -728,7 +728,7 @@ static void hlua_queue_init(lua_State *L)
 
 	hlua_class_function(L, "__gc", hlua_queue_gc);
 
-	class_queue_ref = luaL_ref(L, LUA_REGISTRYINDEX);
+	class_queue_ref = hlua_register_metatable(L, CLASS_QUEUE);
 }
 
 int hlua_fcn_new_stktable(lua_State *L, struct stktable *tbl)