Mortgage rates went down slightly last week.  Freddie Mac reported the following national averages for  mortgage rates for the week ending March 6: 30-year fixed-rate mortgages: averaged 4.28 percent, with an average 0.7 point, dropping from last week’s 4.37 percent average. Last year at this time, 30-year rates averaged 3.52 percent. 15-year fixed-rate mortgages: averaged…