With Maurice Gibb's death in 2003, followed by Robin Gibb's in 2012, the Bee Gees' long ride on the pop charts seemed to be over. But now the remaining member of the group, Barry Gibb, is back on tour, joined not by his brothers but by his son, Stephen. Anthony Mason goes on the road with Gibb, and talks with him about his music, his family, and his pop legacy.