doc: Don't use @table @qcode to avoid problems with Texinfo 5.2. * plot.txi: Replace "@table @qcode" with "@table @asis". Use "@item @qcode{xx}" for each table item. * file-io.cc (Ffread): Replace "@table @qcode" with "@table @asis". Use "@item @qcode{xx}" for each table item. * validateattributes.m: Replace "@table @qcode" with "@table @asis". Use "@item @qcode{xx}" for each table item.