traces: show the stack after reading a token

Currently, if we have long rules and series of shift, we stack states
without showing stack.  Let's be more incremental, and do how the Java
skeleton does.

* data/skeletons/lalr1.cc, data/skeletons/lalr1.d,
* data/skeletons/yacc.c:
Here.
Adjust test cases.
* tests/torture.at (AT_DATA_STACK_TORTURE): Disable stack traces: this
test produces a very large stack, and showing the stack each time we
shift a token goes quadatric.

tests/torture.at

@@ -417,7 +417,6 @@ AT_DATA_GRAMMAR([input.y],
 %}
 ]$2[
 %define parse.error verbose
-%debug
 %token WAIT_FOR_EOF
 %%
 exp: WAIT_FOR_EOF exp | ;
@@ -457,7 +456,7 @@ main (int argc, const char **argv)
   int count;
 ]m4_bmatch([$2], [api.push-pull both],
 [[  yypstate *ps = yypstate_new ();
-]])[  yydebug = 1;
+]])[
   for (count = 0; count < 2; ++count)
     {
       int new_status;