#369 undecipherable_subject_tag not properly encoded in subject

[Fedor Piecka]

When this tag is applied to a message, the subject encoding is not properly set. This tag is added in front of encoding specification and so breaks subject.

Example:

This setting

$undecipherable_subject_tag = 'WARNING: Unchecked encrypted attachment(s) *** ';

produces this

Subject: WARNING: Unchecked encrypted attachment(s) ***
=?iso-8859-1?Q?Statement for 2008-10-31?=

Problem is probably visible with other "subject insertion" settings too...