Bug with subject mime encoding

Issue Summary

There is error while seunding mail with letter subject.
It's not mime encoded that's why there are problems with national characters.
for 6.x module in function drupal_mail_wrapper
Line 480: $mail->Subject = $subject;
must be $mail->Subject = mime_header_encode($subject);

There is a same error for 5.x version of module.

Because wrong subjects sometimes users can not read them.