(Reuters) - British broadcaster David Frost, a master of the television interview, famed for coaxing an apology for Watergate from Richard Nixon, has died suddenly, his family said on Sunday. Aged 74, he had a heart attack late on Saturday aboard a luxury cruise liner where he had a speaking engagement. His sudden death brought tributes from international celebrities and political leaders, many of whom called him a good friend as well as an acute interrogator. "David Frost died of a heart attack last night aboard the Queen Elizabeth, where he was giving a speech," his family said in a...