THE MOSQUITO COAST "The Mosquito Coast" reunites Harrison Ford and Peter Weir after "Witness," for which they both received Academy Award nominations. Ford's performance may make him a dark horse for such a nomination in this long-anticipated film however, Weir is unlikely to receive similar accolade. Best box-office prospects for this clamorous Warner Bros. release may be a few years down the road - whenever the country returns to a 60s-type, anti-establishment period. Right now, word of mouth will be poisonous. Based on Paul Theroux's well-regarded 1982 novel, this film adaptation has brought to the screen some of the least appealing parts of the book's lead character, a b