PHILADELPHIA, Dec 21 (Reuters) - Now that early-stage takeover offers are in for No. 2 U.S. newspaper publisher Knight Ridder (KRI.N: Quote, Profile, Research), interested bidders are working to build alliances as the slow-moving sale process moves into its second round, according to sources close to the process. Knight Ridder, which has a current market value of more than $4.2 bilion, has...