The extreme opposites within Kevin Smith’s filmmaking personality coexist in “Zack and Miri Make a Porno,” to hit-and-miss effect. Yes, there is a ton of sex as the title would suggest, including one scene that is so incredibly wrong, words don’t even begin to describe it. A proliferation of raw, raunchy dialogue has always been one of the writer-director’s preferred tactics, dating back to his pioneering 1994 debut, “Clerks,” and that’s certainly true this time, as well – actually, it’s more relevant than usual.