commit 8e1adff95993effaa22129ff34b4570b755434ac

Author: Sergey Vojtovich <svoj@mariadb.org>

Date:   Sun Jan 21 14:10:06 2018 +0400

    Simplified away ReadView::complete()

    It was supposed to be called out of mutex, but nevertheless was called

    under trx_sys.mutex for normal threads adding one extra condtion in

    critical section.

commit 4dc30f3c170b9deab1ff0b472930baba5c65b01c

Author: Sergey Vojtovich <svoj@mariadb.org>

Date:   Sat Jan 20 17:45:42 2018 +0400

    MDEV-15019 - InnoDB: store ReadView on trx

    This will allow us to reduce critical section protected by

    trx_sys.mutex:

    - no need to maintain global m_free list

    - eliminate if (trx->read_view == NULL) condition.

    On x86_64 sizeof(Readview) is 144 mostly due to padding, sizeof(trx_t)

    with ReadView is 1200.

    Also don't close ReadView for read-write transactions, just mark it

    closed similarly to read-only.

    Clean-up: removed n_prepared_recovered_trx and n_prepared_trx, which

    accidentally re-appeared after some rebase.