DB/Schema: Add index to characters.character_pet.slot. Prevents deadlocks when operating on this table.

sql/base/characters_database.sql

@@ -743,7 +743,8 @@ CREATE TABLE `character_pet` (
   `resettalents_time` int(10) unsigned NOT NULL DEFAULT '0',
   `abdata` text,
   PRIMARY KEY (`id`),
-  KEY `owner` (`owner`)
+  KEY `owner` (`owner`),
+  KEY `idx_slot` (`slot`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='Pet System';
 /*!40101 SET character_set_client = @saved_cs_client */;