NEW YORK (AFX) - The world's biggest stock exchange will open for trading Friday even if officials have to crank up back-up emergency power generators, a New York Stock Exchange (NYSE) spokeswoman said. The exchange, which processes more than 1.3 bln share deals on an average day, can fully function on its back-up generators, she said. The exchange oversees some 35 bln dollars worth of transactions each day, and is due to open for business at 9:30 am (1330 GMT). New York city was left without electricity in Thursday's sudden power outage and remained blacked out late into the evening,...