core: remove value for first #define in headers, add "PLUGIN" in plugin headers

src/plugins/lua/weechat-lua-api.h

@@ -18,8 +18,8 @@
  * along with WeeChat.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef WEECHAT_LUA_API_H
-#define WEECHAT_LUA_API_H 1
+#ifndef WEECHAT_PLUGIN_LUA_API_H
+#define WEECHAT_PLUGIN_LUA_API_H
 
 extern struct luaL_Reg weechat_lua_api_funcs[];
 extern struct t_lua_const weechat_lua_api_consts[];
@@ -32,4 +32,4 @@ extern int weechat_lua_api_buffer_close_cb (const void *pointer,
                                             void *data,
                                             struct t_gui_buffer *buffer);
 
-#endif /* WEECHAT_LUA_API_H */
+#endif /* WEECHAT_PLUGIN_LUA_API_H */