Description:
------------
Some of the array_* functions that compare elements in multiple arrays do so by 
(string)$elem1 === (string)$elem2.

If $elem1 or $elem2 is an array, then the array to string notice is thrown.

Two examples of functions that can throw this are array_intersect() and 
array_diff().

If these functions are not expected to take arrays with other arrays as values, 
this should be mentioned on the documentation pages.

Test script:
---------------
<?php
$left = array('b', array('a'));
$right = array('a', 'd');
print_r(array_intersect($left, $right));
print_r(array_diff($left, $right));


Expected result:
----------------
Array
(
)
Array
(
    [0] => b
    [1] => Array
        (
            [0] => a
        )

)


Actual result:
--------------
PHP Notice:  Array to string conversion in /Users/simon/test.php on line 4
PHP Notice:  Array to string conversion in /Users/simon/test.php on line 4
PHP Notice:  Array to string conversion in /Users/simon/test.php on line 5
PHP Notice:  Array to string conversion in /Users/simon/test.php on line 5
PHP Notice:  Array to string conversion in /Users/simon/test.php on line 5

Notice: Array to string conversion in /Users/simon/test.php on line 4

Notice: Array to string conversion in /Users/simon/test.php on line 4

Array
(
)

Notice: Array to string conversion in /Users/simon/test.php on line 5

Notice: Array to string conversion in /Users/simon/test.php on line 5

Notice: Array to string conversion in /Users/simon/test.php on line 5

Array
(
    [0] => b
    [1] => Array
        (
            [0] => a
        )

)