glr2.cc: example: use objects (not pointers) to represent the AST

Currently we are using pointers.  The whole point of
glr2.cc (vs. glr.cc) is precisely to allow genuine C++ objects to be
semantic values.  Let's make that work.

* data/skeletons/glr2.cc (glr_state::glr_state): Be sure to initialize
yysval.
(glr_state): Add copy-ctor, assignment and dtor.
(glr_state::copyFrom): Be sure to initialize the destination if it was
not.
(glr_state::~glr_state): Destroy the semantic value.
* examples/c++/glr/ast.hh: Rewrite so that we use genuine objects,
rather than a traditional OOP hierarchy that requires to deal with
pointers.
With help from Bruno Belanyi <bruno.belanyi@epita.fr>.
* examples/c++/glr/c++-types.yy: Remove memory management.
Use true objects.
(main): Don't reach yydebug directly.

* examples/c++/glr/local.mk: We need C++11.

THANKS

@@ -34,6 +34,7 @@ Bob Rossi                 bob@brasko.net
 Brandon Lucia             blucia@gmail.com
 Brooks Moses              bmoses@google.com
 Bruce Lilly               blilly@erols.com
+Bruno Belanyi             bruno.belanyi@epita.fr
 Bruno Haible              bruno@clisp.org
 Charles-Henri de Boysson  de-boy_c@epita.fr
 Christian Burger          cburger@sunysb.edu