WL#4968: Apply Google IO thread and max merged IO patch to Server

Affects: Server-5.4   —   Status: Complete   —   Priority: Medium

MySQL 5.4.0:
To improve the InnoDB I/O subsystem's ability to make more effective 
use of available I/O capacity, apply the Google IO thread and max 
merged IO patches from the launchpad tree 5.1-patches maintained by 
Mark Callaghan:
http://code.google.com/p/google-mysql-tools/wiki/InnodbAsyncIo
Applied to MySQL 5.4.0.

Community contribution; for details, follow the link to launchpad:
http://code.google.com/p/google-mysql-tools/wiki/InnodbAsyncIo
and the MySQL 5.4.0 description:
http://dev.mysql.com/doc/mysql-5.4-features/en/innodb-io-changes.html

Patch adds:
* innodb_max_merged_io - Max number of IO requests merged to issue large IO from
background IO threads
* innodb_read_io_threads - the number of background IO threads for read prefetch
requests
* innodb_write_io_threads - the number of background IO threads for writing
dirty pages from the buffer cache 
Community contribution; no further LLD needed.