DIYARBAKIR, Turkey — Just when it seemed Turkey was getting serious about the fight against the Islamic State group, it has turned its military focus to pounding its old foe: the Kurdish rebels. In Turkey’s Kurdish heartland, the government’s renewed military onslaught against the rebels has left many people crying treachery – with suspicions rife that Turkey used a brief offensive against IS as a cover to launch a broad attack against the Kurdistan Workers Party, or PKK.