LONDON, Nov 20 (Reuters) - Investors have rarely been more bearish about oil prices as a slowing economy and an increase in non-OPEC output lead them to conclude OPEC⁺ production cuts will not prevent a rise in inventories.Hedge funds and other money managers sold the equivalent of 7 million barrels in the six most important petroleum-related futures and options contracts over the seven days ending on Nov. 14.Fund managers had sold petroleum in seven of the last eight weeks cutting their position by a total of 338 million barrels since...