Black Fridays by Michael Sears Putnam, $25.99, 341 pages, ISBN 978-0-399-15866-7 Back in the nineteenth century, Mark Twain wrote, “There is no distinctly American criminal class . . . except Congress.”  If he was still living today, he might amend that to say, “. . . except Congress and Wall Street Operators,” because as anyone who pays the least bit of attention to the news knows, hardly a month