WASHINGTON — In his new book, retired U.S. Supreme Court justice John Paul Stevens calls for no fewer than six changes to the Constitution, two of which are directly related to guns. Others would abolish the death penalty, make it easier to limit spending on elections and rein in partisan drawing of electoral districts. His proposed amendments generally would overrule major Supreme Court decisions he disagrees with, including ones on guns and campaign finance in which he dissented. It’s his second book …