make a better effort to avoid walking through system code.

pl/boot.yap

@@ -1170,7 +1170,7 @@ throw(Ball) :-
 % just leave this around to show  the debugger.
 %
 '$notrace'(M:G) :-
-	'$execute0'(G, M).
+	'$execute_nonstop'(G, M).
 
 '$oncenotrace'(M:G) :-
-	'$execute0'(G, M), !.
+	'$execute_nonstop'(G, M), !.

pl/debug.yap

@@ -465,6 +465,9 @@ debugging :-
         '$system_predicate'(G,M),
 	\+ '$is_metapredicate'(G,M), !,
 	'$execute'(M:G).
+'$spycall'(G, M, _, _) :-
+        '$system_module'(M), !,
+	'$execute'(M:G).
 '$spycall'(G, M, _, _) :-
         '$tabled_predicate'(G,M),
 	 !,

pl/modules.yap

@@ -661,4 +661,3 @@ abolish_module(_).
 	'$conj_has_cuts'(G3, DCP, NG3, OK).
 '$conj_has_cuts'(G,_,G, _).
 
-

pl/signals.yap

@@ -35,7 +35,31 @@
 % don't creep on meta-call.
 '$do_signal'(sig_creep, [M|G]) :-
 	'$creep_allowed', !,
-        '$start_creep'([M|G]).
+	(
+	 ( G = '$notrace'(G0) ;  G = '$oncenotrace'(G0) ; G = '$execute0'(G0) ; '$system_module'(M), G = G0 )
+	->
+	 (
+	  '$execute_nonstop'(G0,M),
+	  '$signal_creep'
+	 ;
+	  '$signal_creep',
+	  fail
+	 )
+	;
+	 '$start_creep'([M|G])
+	).
+% 
+'$do_signal'(sig_creep, [M|G]) :-
+	( G = '$notrace'(G0) ;  G = '$oncenotrace'(G0) ; G = '$execute0'(G0) ; '$system_module'(M), G = G0 ),
+	!,
+	(
+	 '$execute_nonstop'(G0,M),
+	 '$signal_creep'
+	;
+	 '$signal_creep',
+	 fail
+	).
+% 
 '$do_signal'(sig_creep, [M|G]) :-
         '$signal_creep',
 	'$execute_nonstop'(G,M).