By Saud Mehsud DERA ISMAIL KHAN, Pakistan (Reuters) - Islamic State on Monday claimed responsibility for the suicide bombing of a political rally in northwest Pakistan held by a religious group allied to the government as the death toll from the attack rose to 45. The bomber struck at a gathering on Sunday of the conservative Jamiat Ulema Islam-Fazl (JUI-F) party, which is known for its links to hardline Islamists but which condemns militants seeking to overthrow the Pakistani government. The attack in the Bajaur district of northwest Pakistan, near the border with Afghanistan, compounded secu...