Description:
------------
When using the flag HTTP_URL_JOIN_QUERY, the function http_build_url fails issuing a warning when there is more than one query argument to join and the php.ini directive arg_separator.output is not in the format of an html entity.

Test script:
---------------
<?php
ini_set('arg_separator.output','&');
$result = http_build_url(
    'http://example.com/?a=b',
    array('query' => 'c=d'),
    HTTP_URL_JOIN_QUERY
);
?>
Expected Result: http://example.com/?a=b&c=d
Actual Result: <?php echo $result; ?>


Expected result:
----------------
Expected Result: http://example.com/?a=b&c=d
Actual Result: http://example.com/?a=b&c=d

Actual result:
--------------
Expected Result: http://example.com/?a=b&c=d
Actual Result: http://example.com/?a=b