Motley Fool: After months of speculation about what oil price would break the back of shale drillers, we finally have that number: $30 a barrel. At least that's the price at which Bakken shale drillers Oasis Petroleum (NYSE:OAS), Whiting Petroleum (NYSE:WLL) and Continental Resources (NYSE:CLR) can no longer keep drilling in the oil play that really turned around America's oil production. That was abundantly clear after reviewing their plans for 2016, with each company basically winding down operations in the...