rewrite the printing of Lazy values in toplevel/genprintval.ml

The code previously used Lazy.is_val to know whether the value was
already-evaluated (and, in this case, Lazy.force to extract this value
and print it more precisely). But it lies inside a functor that is
instantiated over different implementations of Obj, while
Lazy.{is_val,force} force the use of the Obj module of the standard
library. This could cause segfaults when this code is called from the
debugger, which instantiates it with a different Obj module talking
over a socket.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15656 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
rewrite cycle-detection in genprintval.ml to use O instead of Obj

(see previous commit)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15657 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
ocamldebug: fix printing of variables of lazy type

"print a" in ocamldebug when a is a forced lazy value segfaults on all
OCaml versions I tested it on. This comes from the fact that the
debugcomm.ml re-implementation of the Obj module (talking over the
debugging socket) implements Obj.tag without special-casing integers
(that is, testing is_block first), and always assumes its input is
a block.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15658 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02