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.

examples/c/calc/calc.y

@@ -34,6 +34,7 @@ input:
 
 line:
   '\n'
+  | 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' 'a' { printf ("a\n"); }
 | expr '\n'  { printf ("%.10g\n", $1); }
 | error '\n' { yyerrok; }
 ;