MDEV-5834: Merge Kakao Defragmentation implementation to MariaDB 10.1

    Merge https://github.com/kakao/mariadb-10.0 that contains Facebook's
    implementation for defragmentation

    facebook/mysql-5.6@a2d3a74
    facebook/mysql-5.6@def96c8
    facebook/mysql-5.6@9c67c5d
    facebook/mysql-5.6@921a81b
    facebook/mysql-5.6@aa519bd
    facebook/mysql-5.6@fea7d13
    facebook/mysql-5.6@09b29d3
    facebook/mysql-5.6@9284abb
    facebook/mysql-5.6@dbd623d
    facebook/mysql-5.6@aed55dc
    facebook/mysql-5.6@aad5c82

    This version does not add new SQL-syntax and new handler API function.
    Instead optimize table is mapped to defragment table if
    innodb_defragment=ON, by default the feature is off.

    Contains changes authored by Sunguck Lee (Kakao).