Description:
------------
mysqli_get_warnings only ever returns a single warning, even if more 
than one is available.
Though its name implies a plural response, it doesn't deliver one.

Reproduce code:
---------------
Do this in a mysql CLI:

CREATE TABLE `blah` (
  `x` varchar(100) NOT NULL,
  `y` varchar(100) NOT NULL,
  `z` varchar(100) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

INSERT INTO blah SET z = '1';
Query OK, 1 row affected, 2 warnings (0.00 sec)

mysql> show warnings;
+---------+------+----------------------------------------+
| Level   | Code | Message                                |
+---------+------+----------------------------------------+
| Warning | 1364 | Field 'x' doesn't have a default value | 
| Warning | 1364 | Field 'y' doesn't have a default value | 
+---------+------+----------------------------------------+

Now do the same insert from PHP then call mysqli_get_warnings() (approximate code):

mysqli_query($db, "INSERT INTO blah SET z = '1'");
$a = mysqli_get_warnings($db);
var_dump($a);

Expected result:
----------------
I'd want something like this:

array (2) {
object(mysqli_warning)#4 (3) {
  ["message"]=>
  string(38) "Field 'x' doesn't have a default value"
  ["sqlstate"]=>
  string(5) "HY000"
  ["errno"]=>
  int(1364)
},
object(mysqli_warning)#5 (3) {
  ["message"]=>
  string(38) "Field 'y' doesn't have a default value"
  ["sqlstate"]=>
  string(5) "HY000"
  ["errno"]=>
  int(1364)
}
}

Actual result:
--------------
object(mysqli_warning)#4 (3) {
  ["message"]=>
  string(38) "Field 'x' doesn't have a default value"
  ["sqlstate"]=>
  string(5) "HY000"
  ["errno"]=>
  int(1364)
}