Freddie Mac reported this morning that interest rates on 30-year fixed-rate mortgages averaged 4.57 percent this week. That’s down a hundredth of a percentage point from last week’s average rate, which was already at record lows.   Freddie Mac has been tracking 30-year-fixed-rate mortgages for 39 years, and the past three weeks have shown record-setting lows for the most popular type of home loan.