* Tunisia is major source of Jihadi fighters in Syria, Iraq * Political transition allowed extremism to surface * Marginalisation a factor, but many are middle class By Patrick Markey and Tarek Amara SOUSSE, Tunisia, **v 21 (Reuters) - Tunisians were used to seeing Nidhal Selmi belting around a stadium, proudly sporting his country's red and white colours as a defender on the national football squad. So it was a shock when he appeared in a camouflage jacket with a Khalashnikov rifle across his thigh in a photograph from Syria posted online shortly before he was killed fighting there. ...