LONDON, July 10 (Reuters) - Portfolio investors tip-toed back into crude oil as Saudi Arabia extended its unilateral production cut for at least another month, dissipating some of the extreme pessimism gripping the market at the end of June.Hedge funds and other money managers purchased the equivalent of 47 million barrels in the six major petroleum futures and options contracts over the week ending on July 3-4.Buying was concentrated in crude (+52 million barrels) with purchases of Brent (+25 million) and NYMEX and ICE WTI (+27 million), according to exchange...