Bug #56545 - Speed up topic move operation by adding an index for topic_id on the topics track table.

git-svn-id: file:///svn/phpbb/branches/phpBB-3_0_0@10462 89ea8834-ac86-4346-8a33-228a782c2dd0

phpBB/install/database_update.php

@@ -900,6 +900,11 @@ function database_update_info()
 			'drop_keys'		=> array(
 				LOG_TABLE			=> array('log_time'),
 			),
+			'add_index'		=> array(
+				TOPICS_TRACK_TABLE	=> array(
+					'topic_id'		=> array('topic_id'),
+				),
+			),
 		),
 	);
 }