BERLIN (Reuters) - German Chancellor Angela Merkel emerged as the clear winner of the only television debate with her center-left challenger Martin Schulz three weeks before a federal election, a poll showed on Sunday. The survey by Infratest Dimap for ARD television showed that 49 percent viewed Merkel as being more credible while 29 percent favored Schulz. Merkel s overall performance was viewed as more convincing by 55 percent, compared to 35 percent for Schulz. 