Washington Mutual Bank’s buying spree this year has had a noticeable impact on the mortgage giant’s standing in the thrift industry. And by early next year, WaMu could account for nearly one third of the thrift industry’s total mortgage production. According to recently released numbers from the Office of Thrift Supervision, WaMu accounted for a hefty 20 percent of the industry’s total $287.76 billion in mortgage originations during the first three quarters of 2001. WaMu