Merge WebScaleSQL InnoDB patches

Consider at least following:

• Add count of lock waits and lock wait timeouts to table_statistics: https://github.com/facebookarchive/mysql-5.1/commit/4678f63b4d5df90ec11f51e8038509905babc064

• Bring back adaptive flushing from official InnoDB : https://github.com/facebookarchive/mysql-5.1/commit/6cc926075ab425110abae022616a298587c33816

• Per page stats for IS.table_stats: https://github.com/facebookarchive/mysql-5.1/commit/159d632a3361a338937b3d969b8788520107eebd

• Global write/read from memory buffer per page type stats: https://github.com/facebookarchive/mysql-5.1/commit/f9b082f6af9cf09d570ad664b9edec8953aa2478 and https://github.com/facebookarchive/mysql-5.1/commit/755e638d79430bf911100b72dbfa16434fb5be50

• Make InnoDB call fsync() periodically when creating a new file: https://github.com/facebookarchive/mysql-5.1/commit/1d2c2183f67e48dd4d3fad99e5427ec32d4ddbaa (FusionIO)

• Attempt to fix flushing: https://github.com/facebookarchive/mysql-5.1/commit/ca473983efff7638ad89fef9ab73ab433448c42c (? needed ?)

• Fix LRU flushing, thereby fixing xtrabackup slowness: https://github.com/facebookarchive/mysql-5.1/commit/f70e3cee598b9a628264ca3414cab543100a13ce

• Add Facebooks's integrated version of xtrabackup: https://github.com/facebook/mysql-5.6/commit/a6662524643ec1236d74151bc3936da6169721bd

• Add logical read-ahead to InnoDB: https://github.com/facebook/mysql-5.6/commit/f8e361952612d00979f7cf744f487e48b15cb5a6

• Merge aio page read requests: https://github.com/facebook/mysql-5.6/commit/f9d1a5332eb2c82c028638d3b93b5a3592a69ffa

• Add mysqldump support for logical read ahead: https://github.com/facebook/mysql-5.6/commit/f69a4ea522bce24e4cdcc7696d5fad29587cf87a
• Introduce a reduced doublewrite mode, handling error detection only: https://github.com/webscalesql/webscalesql-5.6/commit/06c931f7f7b6b69ee57dabbeee08d19e9ef6f25d ?