Description:
------------
mysqli_commit does not work when using mysqlnd + MYSQLI_ASYNC + autocommit=false.

The main transaction gets commited, but everything executed via MYSQLI_ASYNC does not get commited.

Test script:
---------------
https://gist.github.com/sshilko/2119c6b87ff4887142ab

Expected result:
----------------
$ time php async.php 
Doing insert AUTOCOMMIT=FALSE: 
INSERT INTO asynctest (`date`, `user_id`) values ('2015-05-18', '1431964720')
Insert done
Doing select: 
Array
(
    [0] => Array
        (
            [COUNT(*)] => 1
        )

)
Doing insert AUTOCOMMIT=TRUE: 
INSERT INTO asynctest (`date`, `user_id`) values ('2015-05-18', '1431964720')
Insert done
Doing select: 
Array
(
    [0] => Array
        (
            [COUNT(*)] => 2
        )

)

real    0m0.032s
user    0m0.013s
sys     0m0.003s


Actual result:
--------------
$ time php async.php 
Doing insert AUTOCOMMIT=FALSE: 
INSERT INTO asynctest (`date`, `user_id`) values ('2015-05-18', '1431964720')
Insert done
Doing select: 
Array
(
    [0] => Array
        (
            [COUNT(*)] => 0
        )

)
Doing insert AUTOCOMMIT=TRUE: 
INSERT INTO asynctest (`date`, `user_id`) values ('2015-05-18', '1431964720')
Insert done
Doing select: 
Array
(
    [0] => Array
        (
            [COUNT(*)] => 1
        )

)

real    0m0.032s
user    0m0.013s
sys     0m0.003s