New field "network" in item table to speed up the system.

database.sql

@@ -562,6 +562,7 @@ CREATE TABLE IF NOT EXISTS `item` (
   `forum_mode` tinyint(1) NOT NULL DEFAULT '0',
   `mention` tinyint(1) NOT NULL DEFAULT '0',
   `last-child` tinyint(1) unsigned NOT NULL DEFAULT '1',
+  `network` char(32) NOT NULL,
   PRIMARY KEY (`id`),
   KEY `uri` (`uri`),
   KEY `uid` (`uid`),
@@ -593,6 +594,7 @@ CREATE TABLE IF NOT EXISTS `item` (
   KEY `mention` (`mention`),
   KEY `resource-id` (`resource-id`),
   KEY `event_id` (`event-id`),
+  KEY `network` (`network`),
   FULLTEXT KEY `title` (`title`),
   FULLTEXT KEY `body` (`body`),
   FULLTEXT KEY `allow_cid` (`allow_cid`),