The country life in which Jane Austen's aristocratic characters so wittily conduct their marital maneuverings was, like it or not, often funded by the profits from the slave trade. This adaptation of the 1814 novel Mansfield Park brings that dirty fact to the fore, adding unexpected heft to Austen's delightful ''are they the only ones who don't know'' romance between poor relation Fanny (O'Connor) and her handsome cousin Edmund (Miller).