By Saul Hansell February 26, 2009 6:10 am February 26, 2009 6:10 am It may be no surprise that the best-selling computer book so far this year is “iPhone: The Missing Manual,” by my colleague David Pogue (O’Reilly, 2007). But here is something that did surprise me: The most popular edition of this book isn’t on paper or the PDF file that O’Reilly Media also sells. It is the downloadable applicatio