It's swan song time for Swans.With last month's release of a new album, "The Glowing Man," and its current tour, founder and leader Michael Gira plans to retire the experimental rock group, at least as we've known it since 1982. "I'm going to continue to make music under the name of Swans, but I'm just going to have revolving members according to what the material calls for," Gira, 62, explains by phone from Providence, R.