Premarket: World shares edge up in nervy trade ahead of debt limit talks

Global shares edged up on Tuesday, while the U.S. dollar eased back from five-week highs as U.S. lawmakers prepared for another round of talks to resolve the deadlock over the government's borrowing limit. The weaker dollar supported crude oil and equities, although investors were wary of crucial U.S. government debt-ceiling negotiations, with a little more than two weeks to go before the government could run short of money to pay its bills. Investors have dumped short-term U.S. Treasuries that mature around the "X date" – the point beyond which the government runs out of money to pay its bills without…