Click to email a link to a friend (Opens in new window) Click to share on Twitter (Opens in new window) Click to share on Facebook (Opens in new window) Barry Manilow has to pinch himself. After more than 20 years in the works, his long-awaited musical “Harmony” — co-written with Bruce Sussman – is finally Broadway bound. “Standing in front of the theater is really surreal,” the “Mandy” warbler, 79, exclusively told Page Six at the Ethel Barrymore Theater, where the show will open in October. “It’s really happening!” The show was first staged in 1997 at the La...