Description:
------------
if i receive an email with this content type:
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

i can use imap_fetchstructure to recontruct the original email content type, but then when i use imap_mail_compose, the format property is lost


Reproduce code:
---------------
$envelope["from"] = "from@example.net";
$part["type"] = 0;
$part["subtype"] = "PLAIN";
$part["charset"] = "iso-8859-1";
$part["format"] = "flowed";
$part["contents.data"] = "text";
$body[] = $part;
$mail = imap_mail_compose($envelope, $body);
echo $mail;


Expected result:
----------------
using imap_fetchstructure, part of the returning object is
    [parameters] => Array
        (
            [0] => stdClass Object
                (
                    [attribute] => charset
                    [value] => iso-8859-1
                )
            [1] => stdClass Object
                (
                    [attribute] => format
                    [value] => flowed
                )
        )

by fetching these parameters i get information to compose the mail such as line 4 and 5 of example script.
then using imap_mail_compose it should generate a content-tpye like the one from the original mail i.e.:
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Actual result:
--------------
imap_mail_compose, using php source code above generete this content-type:

Content-Type: TEXT/PLAIN; CHARSET=iso-8859-1


format=flowed is missing