In case the header is not 7bit clean, gtk20 has problems displaying it
correctly (because then it is not utf8 valid as well)
Force converting the header and the xover data (usenet) to utf-8 in case
it isn't 7bit clean by assuming the header was written in the charset
locale(1) reports. That might be wrong, but I see no other way.
We can't detect the charset in which the header was written in (for
example, xover data doesn't have any informations in it about content-type)
because Content-Type only affecty the message-body.

Approved By: maintainer (implicit)
Taken From: sylpheed-claws gtk2 CVS branch