A Senate committee today (TUES) voted to change a law beneficial to Northwest Airlines after some legislators charge the airline duped them into passing the law. Minnesota Public Radio's Martin Kaste reports: One week ago, legislators discovered that an apparently technical change they made to the state's franchise law last year was actually of great potential benefit to Northwest Airlines. The change, which was retroactive, gave Northwest a defense against a $30-million-dollar lawsuit filed against it by two small airlines in Maine. Senator Allan Spear says he was shocked to discover that he and his colleagues had inadvertently meddled in an ongoing court case: ((We have a long, admirable tradition in this Legislature that we don't pass legislation that affects pending lawsuits! And that's what