be more like the interpreter in signalling wrong-num-args

* libguile/vm-engine.c: Call scm_wrong_num_args in the wrong-num-args
  case, to be more like the interpreter.

* libguile/vm-engine.h (ASSERT): New macro.

* libguile/vm-i-system.c (apply, goto/apply): Assert that nargs >= 2,
  because the compiler should always feed us correct instructions.
  (call/cc): If no values are returned to the continuation, signal
  no_values instead of wrong_num_args.

libguile/vm-engine.h

@@ -127,6 +127,15 @@
  * Cache/Sync
  */
 
+#define ENABLE_ASSERTIONS
+
+#ifdef ENABLE_ASSERTIONS
+# define ASSERT(condition) if (SCM_UNLIKELY (!(condition))) abort()
+#else
+# define ASSERT(condition)
+#endif
+
+
 #define CACHE_REGISTER()			\
 {						\
   ip = vp->ip;					\