JOHANNESBURG (Reuters) - South Africa's rand eased on Friday, pressured by economic concerns after the World Bank cut its growth forecast and data showed credit demand falling more than expected. * At 0615 GMT, the rand traded 0.4 percent weaker at 13.93per dollar. * World Bank cuts South Africa's growth forecast, S&P sayspolitical turmoil a concern. * Zuma urges ministries to tackle 'mayhem' at universitiesas student protests expose ANC's weak policy record. * U.S. data due next week causing market jitters. Chance ofa Federal Reserve rate hike in December seen 50-50. * Yield for the benchmark government bond due in 2026 up 0.5basis points to 8.72 percent. (Reporting by Joe Brock; Editing by Ed Cropley)