Description:
------------
Using the cURL to send files with custom content-type (eg.: "@filename;type=content-type") does not work, because undesirable "type=" string is preprended to the actual content-type.

Reproduce code:
---------------
test.php:
---------

$data = array('file' => '@sheet.xls;type=application/vnd.ms-excel');

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://localhost/upload.php');
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
curl_exec($ch);

echo curl_error($ch);


upload.php:
-----------
print_r($_FILES);


Expected result:
----------------
Array
(
    [file] => Array
        (
            [name] => sheet.xls
            [type] => application/vnd.ms-excel
            [tmp_name] => /var/tmp/php21KVfg
            [error] => 0
            [size] => 1192
        )

)


Actual result:
--------------
Array
(
    [file] => Array
        (
            [name] => sheet.xls
            [type] => type=application/vnd.ms-excel
            [tmp_name] => /var/tmp/php21KVfg
            [error] => 0
            [size] => 1192
        )

)