Code review comment for lp:~hrvojem/percona-server/bug1056603-5.1

Hrvoje,

Few comments:

- There's a difference between internal InnoDB tables naming and the
  corresponding I_S tables exposing those internal tables. That is, the
  internal InnoDB tables are called SYS_STATS, SYS_TABLES and
  SYS_INDEXES, while their user-visible I_S counterparts have the
  INNODB_ prefix: INNODB_SYS_STATS, INNODB_SYS_TABLES and
  INNODB_SYS_INDEXES.

So it is technically incorrect to say that "If this option is enabled,
|XtraDB| uses the :table:`INNODB_SYS_STATS` system table to store
statistics of table indexes". It actually uses SYS_STATS, as correctly
described now.

- the patch adds INNODB_SYS_TABLES and INNODB_SYS_INDEXES which is good,
  but it only describes their structure without providing any further
  info, which is not that good :)

- s/the index haven't been used/the index has not been used/