By Daren Butler MURSITPINAR Turkey (Reuters) - Islamic State raised its flag on a building on the outskirts of the Syrian frontier town of Kobani on Monday after an assault of almost three weeks, but the town's Kurdish defenders said its fighters had not reached the city centre. A black flag belonging to Islamic State was visible from across the Turkish border atop a four-storey building close to the scene of some of the most intense clashes in recent days. ...