With a sustainable vision and a thing for dumpster diving, Bronx son Omar Freilla is leading his city's rebirth. By Robert Sullivan Mens' Vogue: You could go looking for an environmental activist somewhere out in the pristine wilderness, maybe living in an old tree he's trying to save. In the case of Omar Freilla, executive director of Green Worker Cooperatives, you head to the South Bronx, a place better known as the pristine wilderness's polar opposite. When it was being burnt to the ground in the seventies, the South Bronx was Exhibit A in the death of cities. Lately, however, it has become proof of the rebirth of cities: The fields of once smoldering rubble are now raising luxury condos, and there is even a hip acronym, SoBro. "Lively, diverse, intense cities," the late urban scholar Jane Jacobs wrote, "contain the seeds of their own regeneration, with energy enough to carry over for problems and needs outside themselves." Freilla, tall and thi