By Pesha Magid SINJIL, West Bank, July 9 (Reuters) - On a cool night in June, some 15 Palestinians from the town of Sinjil in the occupied West Bank gathered on a hilltop to watch the shadowed valleys below for any sign of movement that might signal an impending Israeli settler attack. They are part of a grassroots volunteer group — similar to others in the West Bank — that has stepped in to defend the town from rising settler violence that Palestinians say the Israeli military and their own gov