Proto CC-5013-MM-020: 3-Arm Study to Determine the Efficacy and Safety of Lenalidomide (Revlimid) Plus Low-Dose Dexamethasone When Given Until Progressive Disease or for 18 Four-Week Cycles Versus the Combination of Melphalan Prednisone, and Thalidomide Given for 12 Six Week Cycles in Patients with Previously Untreated Multiple Myeloma Who Are Either 65 Years of Age or older or Not Candidates for Stem Cell Transplantation.