Cory WeaverEric Owens (Porgy) and Laquita Mitchell (Bess)Better than: Being trampled -- in your own seat -- by half the people in your section as they make for the Irish coffee at intermission. More on that later.On the BART ride home after San Francisco Opera's Sunday evening performance of George and Ira Gershwin's Porgy and Bess, I overheard a woman discussing the show with a seatmate who'd apparently just come from Wicked. She declared it "the best opera I've ever seen," largely because she