BOSTON (Reuters) - When it comes to food, Boston is best known for baked beans and clam chowder. But this week, state legislators have engaged in robust debate on Marshmallow Fluff -- a locally made, sugary spread. State Sen. Jarrett Barrios started the tempest in a lunch box when he learned that his son's Cambridge grammar school cafeteria offered Fluff-and-peanut butter sandwiches daily. In a nation where child obesity rates have more than doubled in the past 25 years, Barrios fretted that was not a healthy option. Monday he proposed a law that would allow schools to serve the "Fluffernutters"...