The average rate on a 30-year U.S. mortgage fell again this week, slipping close to its low point so far this year. The decline brings the average long-term mortgage rate to 6.19% from 6.23% last week, mortgage buyer Freddie Mac said Thursday. A year ago, the rate averaged 6.69%. This is the second straight weekly drop in the average rate after three straight increases. It’s now at the lowest level since Oct. 30, when it was at 6.17%, the lowest level in more than a year. Borrowing costs on 15-