WASHINGTON - When Sen. Edward M. Kennedy accepts a public service award from former President Bush next week in Texas, awkward moments are bound to buffet the two chiefs of America's most prominent and powerful political families. The liberal Bay State senator has emerged as the harshest Capitol Hill critic of Bush's conservative son, President George W. Bush. Kennedy actually called Bush a serial liar in a blistering speech last month on Iraq. ``It will be the pink elephant just sitting there in the middle of the room,'' Jim McGrath, a spokesman for the elder Bush, said of the simmering...