Description:
------------
When executing mb_send_mail with headers 
<?
$headers = 'Content-Type: text/plain; charset="UTF-8"';
mb_send_mail('name@example.org', 'The Bug', 'Bla bla bla', $headers);
?>

Error: "Unsupported charset ""UTF-8"" - will be regarded as ascii"

But when i pass charset=UTF-8 its works Okey...


Reproduce code:
---------------
<?
$headers = 'Content-Type: text/plain; charset="UTF-8"';
mb_send_mail('name@example.org', 'The Bug', 'Bla bla bla', $headers);
?>

Expected result:
----------------
ignore quotes in Content-Type: text/plain; charset="UTF-8"

Actual result:
--------------
Error: "Unsupported charset ""UTF-8"" - will be regarded as ascii"