The average rate on a 30-year U.S. mortgage edged lower this week, staying relatively close to its low for the year. The decline brings the average long-term mortgage rate to 6.21% from 6.22% last week, mortgage buyer Freddie Mac said Thursday. A year ago, the rate averaged 6.72%. Borrowing costs on 15-year fixed-rate mortgages, popular with homeowners refinancing their home loans, also fell this week. The rate averaged 5.47%, down from 5.54% last week. A year ago, it averaged 5.92%, Freddie Mac said. ...