Discount grocer Aldi said Wednesday it plans to buy 400 Winn-Dixie and Harveys supermarkets in the southern U.S. Under a proposed merger agreement, Aldi will acquire all outstanding shares of Jacksonville, Florida-based Southeastern Grocers Inc., the parent company of Winn-Dixie and Harveys. Aldi said the deal supports its long-term growth strategy in the U.S., where it expects to have 2,400 …