Leyla Gencer: The very name is exotic. She was an artist of Turkish ancestry who, during the 1950s and 60s, held her own despite the presence of Maria Callas, Renata Tebaldi, Renata Scotto, Montserrat Caballe, and Magda Olivero, all of whom shared roles in her repertoire. Ironically, Gencer has a number of important credits attached…