A Drop of the Hard Stuff  by Lawrence Block Mulholland Books, $25.99, 319 pages, ISBN 978-0-316-17804-4 This week’s MBR is A Drop of the Hard Stuff, by Lawrence Block, a distinguished author of more than fifty novels.  He’s as easy and comfortable to read as a favorite old flannel shirt is to wear beside a warm fire on a nippy fall night. The novel begins with two old friends,