AT the Arlington National Cemetery in Virginia, United States lies a simple grave with a gas-fired eternal flame; a memorial to President John Fitzgerald Kennedy, 1917-1963. This year marks the centenary of his birth. He was born on May 29 1917, scion of the East Coast Brahmin of Massachusetts. His father Joseph Senior came from Irish émigré stock as was his mother Rose Kennedy. The senior Kennedy made an enormous fortune, some would say, from things that were not entirely kosher.