Glencore may step out of shadows with London float

• Publicity-shy commodities empire Glencore plans IPO • Swiss-based company is biggest shareholder in miner Xstrata With its headquarters tucked away in the tiny Swiss village of Baar, it is not surprising that Glencore International has been described as the biggest company you have never heard of. Anonymity is a trademark of the privately owned commodities empire, which was founded nearly 40