U.S. album sales hit 3.97-million last week, the smallest weekly total for album sales since Nielsen SoundScan first began tracking data in 1991, Billboard's Ed Christman and Glenn Peoples report. It's also the first time during that period that weekly sales have fallen below 4 million, they write.Sales for the week ending August 25 fell 18.6%. The best seller was rapper Whiz Khalifa's "Blacc Hollywood" which debuted with 90,000 units, Billboard says. For the first time in more than a year, sales for the soundtrack to Disney's "Frozen" fell below 100,000 units.CD sales have practically vanished, down 19.2% year-over-year, with sales at...