Early gains quickly fizzled into narrow losses Wednesday, despite solid advances by Oracle (ORCL), General Motors (GM) and Mellanox Technologies (MLNX). The S&P 500 dipped 0.2%. The Nasdaq and the Dow Jones industrial average slipped 0.1% each. Volume rose 15% on the Nasdaq and slipped 3% on the NYSE compared with the same time Tuesday. General Motors gapped up more than 8% on news that the mending automaker planned to buy back 200 million shares