With his country gearing up for a hotly contested presidential election early next year the Senegalese singer and songwriter Youssou N’Dour, one of the biggest stars of the “world music” genre, is putting his career on hold to plunge into the political fray. It’s not clear in what capacity — as a candidate for public office himself, or just lending his prestige and support to someone already in the running — or for how long, but he made the announcement over the weekend and set a date to stop performing.