'Parse and decode `Subject` header.'

def set_subject(self):

    _subject = decode_header(self.mail.get(u'Subject', u'No    Subject'))
    self.subject = (_subject[0][0] or u'')
    if _subject[0][1]:
        self.subject = self.subject.decode(_subject[0][1])
    else:
        self.subject = self.subject.decode(u'utf-8')[:140]
    if (not self.subject):
        self.subject = u'No    Subject'
