Description:
------------
When using json_encode with JSON_NUMERIC_CHECK, json_encode still converts all 
array keys to a string, instead of keeping integer keys as integer. However, the 
JSON_NUMERIC_CHECK option does work correctly on all the array values.



Test script:
---------------
<?php
$array = array (
	1	=> "foo",
	5	=> "bar",
	"10"	=> 50,
);

echo json_encode ($array, JSON_NUMERIC_CHECK);
?>

Expected result:
----------------
{1:"foo",5:"bar","10":50}

Actual result:
--------------
{"1":"foo","5":"bar","10":50}