expand meta-predicates before trying to debug them.

pl/debug.yap

@@ -384,8 +384,15 @@ debugging :-
 	fail.
 
 % if we are in 
-'$loop_spy2'(GoalNumber, G, Module, CalledFromDebugger, CP) :- 
+'$loop_spy2'(GoalNumber, G0, Module, CalledFromDebugger, CP) :- 
 /* the following choice point is where the predicate is  called */
+	   (
+             '$is_metapredicate'(G0, Module)
+	   ->
+	    '$meta_expansion'(G0,Module,Module,Module,G,[])
+	   ;
+	     G = G0
+	   ),
 	   b_getval('$spy_glist',[info(_,_,_,Retry,Det)|_]),	/* get goal list		*/
 	   (
 	    /* call port */