By Denny Dyroff, Entertainment Editor, The Times Plain White T’s Frequently, area venues present twin bills where music fans can “double their pleasure and double their fun” at a concert featuring complementary co-headliners. On December 11, fans can “triple their pleasure and triple their fun” when Theatre of the Living Arts (334 South Street, Philadelphia, 215-222-1011, http://www.lnphilly.com)...