Forget the euphemisms, Up the Sandbox is an untidy melange of overproduced, heavy-handed fantasy concerning a married woman’s identity crisis, and laced with boring gallows humor about how bad life is in Manhattan.The novel by Anne Richardson Roiphe has been adapted into a screenplay with very few genuine laughs but an awful lot of straining for cheap guffaws. Barbara Streisand, married to Prof David Selby, is harried by two children and fears the effect on herself and her marriage of accommodating the birth of a third child. Resolution is as inarticulate as the development. Were Streisand to have been working off some old contractual commitment, there would be much sympathy. But this is not the case, since the star is the producer.