AliSQL: [Performance] Issue #40 Optimize performance of semisync

Description:

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This diff includes:

    1. Make semisync buidin to completely remove overhead of plugin lock.

    2. Remove LOCK_log requirement from dump thread

    3. Now user threads can wait for ACK before innodb commit.

        add rpl_semi_sync_master_wait_point to control this behavior(AFTER_COMMIT/AFTER_SYNC)

    4. Add a new ACK thread to handle ACK from slave.

    5. The IO thread flushs master info only when ACK is needed

        add rpl_semi_sync_slave_delay_master to control this behavior

    6. Fix bug#70669, if sync_binlog = 1 ,then notify dump thread after fsync of binlog file.