Live checksums for InnoDB tables

The functionality is to add "LIVE CHECKSUM" for InnoDB tables. That means command
"CHECKSUM TABLE t_innodb_table" returns result almost immediately.

More on design:

The feature is turn on by parameter

innodb_live_checksum=ON | OFF

Functionality works with next pre-requirements:

innodb_file_per_table=1
checksum is stored in .ibd table header

In case of crash - checksum is getting state "UNKNOWN"

To calculate initial checksum one should execute command
ANALYZE TABLE t_innodb_table

The re-calculation of checksum is done in real-time when we change ( insert, delete, update) rows.
This is done in READ-UNCOMMITED way, so new checksum is available even transaction is not committed.

Information about checksums also will be available in INFORMATION_SCHEMA.TABLES_CHECKSUM table