By Isabel Coles and Jonny Hogg ARBIL Iraq/MURSITPINAR Turkey (Reuters) - Iraqi Kurdish forces captured a strategic border crossing and several villages from Islamic State fighters in **rthern Iraq on Tuesday, scoring gains as the militants were pounded by heavy U.S.-led air strikes and the Iraqi army advanced from the south. An Iraqi Kurdish political source said Kurdish peshmerga fighters took control of the Rabia border crossing with Syria in a battle that began before dawn. "It's the most important strategic point for crossing. ...