c++: minor changes

* data/lalr1.cc: Fix oldish comment.
* data/stack.hh: Prefer typename for type names.
Use size() instead of duplicating it.
* examples/variant-11.yy, examples/variant.yy (yylex): Use int,
as this is the type of the semantic value.

TODO

@@ -1,4 +1,10 @@
 * Short term
+** C++
+Move to int everywhere instead of unsigned?  stack_size, etc.  The parser
+itself uses int (for yylen for instance), yet stack is based on size_t.
+
+Maybe locations should also move to ints.
+
 ** Graphviz display code thoughts
 The code for the --graph option is over two files: print_graph, and
 graphviz. This is because Bison used to also produce VCG graphs, but since