By THÉRÈSE MARGOLIS When it comes to hams, Iberians are the top of the line. These succulent, flavorful gammon masterpieces of Spain — produced from the acorn-grazed, black-hoofed Iberian pigs found only in the mountainous southern and southwestern regions of that European nation — are the crème de la crème of fatty cured pork. The history of jamón ibérico is