Jeremy Piven abruptly quit his $15,000 a week gig in the Broadway revival of David Mamet’s Speed-the-Plow last week, when his doctor claimed he had mercury poisoning from all of the sushi he’d been eating. For this story to be true, he would be the first human in recorded history* to get mercury poisoning from eating sushi in this country. Is it time to contact the Guiness Book of World