I have known Paul McGuinness for some 40 years, from before he managed U2. He learned the tricks of a rough trade and graduated as a go-to guru in ethical management. And, hand-on-heart, I have never known Paul McGuinness (or U2) do anything mean or petty. He is worthy but never dull. In the early 1990s, U2 became the most successful rock band in the world – and their most recent world tour had the biggest ever ticket sales by any rock band. I first asked him to sit down with me for a long interview a year ago and…