A jailed Sikh separatist leader is contesting India’s general election from prison and drawing good support, his campaign managers said, in what could become a concern for New Delhi which has sought to stamp out any revival of Sikh militancy. Amritpal Singh, 31, is detained in a high-security prison in Assam, nearly 3,000 km (1,865 miles) from his Khadoor Sahib constituency in Punjab state, where villages and towns are dotted with posters depicting him with swords and bullet-proof vests. Singh was arrested last year and jailed under a tough security law after he and hundreds of his supporters …