Tortilla Flat, by John Steinbeck. New York: Covici, Friede. $2.50. Not since the days of W. W. Jacobs, making his disarming characters out of scoundrels, has there been a book quite like this one. Both Jacobs and Steinbeck must have worked on the assumption that most of us, having a slice or two of Caspar Milquetoast in our systems or a streak that calls for out and out anarchy, are likely to revel in the antics of anyone getting away with what he shouldn’t. The Paisanos of Tortilla Flat get away with agreat deal in their tireless efforts to supply their gullets with red wine.