Saudi Arabia's decision to slash the official selling price for its oil has sparked trader talk of an emerging OPEC price cutting war, as members of the producer group could compete to defend their market share amid ample supplies and tepid demand. Industry and trading sources in the Middle East say there was now a risk of a race to the bottom, at a time when many were calling for unity from members of the Organization of the Petroleum Exporting Countries (OPEC) as it faces one of the steepest price slides since the financial crisis. The group's next meeting in November will be closely-watched to see whether it cuts supply. Benchmark Brent crude prices continued to slide towards $90 a barrel on Thursday…