When the sound of a gunshot pierced the lively hum of a crowded motorcade more than 60 years ago, Clint Hill threw himself across the bodies of President John F. Kennedy and Jacqueline Kennedy.The former Secret Service Agent, whose actions became a defining part of that fatal Dallas day, was laid to rest this week at Arlington National Cemetery — the same burial ground as President Kennedy — with military honors. Hill was 93 when he passed away …