AGREEMENT AND PLAN OF MERGER BY AND AMONG AMERIPATH, INC., PATHOLOGY ASSOCIATES OF INDIANA, P.C. PATHOLOGY ASSOCIATES, P.C. ALAN HALPERIN, M.D. WOJCIECH SZANIAWSKI, M.D. PAUL CHU, M.D. AND MARK JACOBSON, M.D. DATED AS OF DECEMBER 3, 2004