By MELISSA T. CASTRO     It’s one of those old go-to comfort foods for upset tummies or sore throats. Oatmeal – hulled oat grains that have been milled, steel-cut or rolled – has been around for centuries, and is a hardy and wholesome breakfast food, as well as a nutritious additive for breads and pastries, smoothies and soups. “Historically, oatmeal has