LONDON (Reuters) - Stock index futures pointed to a slightly higher open on Wall Street on Thursday. Futures for the S&P 500 and the Dow Jones rose 0.2 percent, while contracts on the Nasdaq 100 were up 0.1 percent at 0852 GMT. European shares also rose as investors took heart from fresh signs that central banks would continue steps to support the world's economy. Revised U.S. GDP data at 1330 GMT is expected to show the U.S. economy grew by 0.5 percent in the fourth quarter, rather than a 0.1 percent contraction as initially estimated. ...