MONTREAL (CP) - It may take a special tax to help fight what one Canadian sociologist calls the "obesogenic food environment" - the junk food that's prominently displayed in supermarkets and schools. Anthony Winson of the University of Guelph said high-sugar and high-fat products are "aggressively promoted" every week in grocery stores. "You can have maybe 20 special displays in a supermarket that are around every corner promoting types of high-sugar, high-fat products, whether they be candy bars or soft drinks," Winson said in an interview. He said the displays are advantageous for retailers because they bring in extra revenue....