Entertainment industry figures have poured millions into California’s Proposition 87, which would impose a tax on oil production to pay for alternative fuels, but the initiative is slipping in the polls. The latest Field Poll shows the measure trailing at 40 percent to 44 percent, a seven point slip from where it was in September. Producer Steve Bing has poured almost $50 million into the Yes on 87, along with Tom Hanks, Julia Roberts and Robert Redford, as well as Alan Horn and Jim Wiatt. Yahoo’s Terry Semel made a $25,000 contribution last week. But they are still outgunned by the No on 87 campaign, financed heavily by oil and energy companies, with a war chest of almost $75 million this year.