Impacted versions: ODOO 10

Problem.
If i print a invoice with a negative amount, the pdf shows a vertical bar instead of a minus symbol.
![image](https://cloud.githubusercontent.com/assets/28800797/26237253/b07fadb0-3c74-11e7-86c2-c8688d82b5a5.png)

I have tried to install a new pdf reader, but with no result.
# 
    # 
    def setUp(self):
        super(TestRelativeDatetime, self).setUp()
        # 
        self.registry('res.lang').load_lang(self.cr, self.uid, 'fr_FR')
    def test_basic(self):
        converter = self.get_converter('datetime', 'relative')
        t = datetime.datetime.utcnow() - datetime.timedelta(hours=1)
        result = converter(t, context={'lang': 'fr_FR'})
        self.assertEqual(result, u"il y a 1 heure")