BUCHAREST, Romania - At first, fans politely applauded the Roma performers sharing a stage with Madonna. Then the pop star condemned widespread discrimination against Roma, or Gypsies — and the cheers gave way to jeers. The sharp mood change that swept the crowd of 60,000, who had packed a park for Wednesday night's concert, underscores how prejudice against Gypsies remains deeply entrenched across Eastern Europe. Despite long-standing efforts to stamp out rampant bias, human rights advocates say Roma probably suffer more humiliation and endure more discrimination than any other people group on the continent. Sometimes, it can be deadly: In...