Northwest Airlines shareholders approved a merger with Delta Air Lines on Thursday morning, while Delta shareholders prepared to meet this afternoon to have their votes tallied. Approval by both carriers' shareholders would be a major milestone toward the close of the deal. The only remaining big hurdle for the deal would be approval from the U.S. Department of Justice. Delta expects the antitrust regulator to issue a decision later this year. If DOJ approves, Delta would close the deal shortly thereafter. ...