It has been decades since Bessie Gaul could walk from her apartment near Bowdoin-Geneva and get fresh food in a high-quality store. But last Saturday morning, she went shopping with a smile as the long-awaited Dorchester Food Coop (DFC) opened its doors on the ground floor of a new building at 195 Bowdoin St. “I’ve been waiting for this for 54 years,” said Gaul, who was with