Mercer International has offered a $26 million stalking horse bid for bankrupt lumber producer Klausner Lumber One LLC’s assets up for sale in an upcoming bankruptcy auction.    In a motion filed with U.S. Bankruptcy Judge Karen B. Owens, Klausner Lumber One LLC said it has secured the stalking horse offer from Mercer after negotiations with another potential bidder fell through. Under the new proposed deal, which is subject to potential better offers at an auction scheduled for later this month, Mercer is set to pay $26 million and assume certain liabilities, court filings said ...