avoid creating new index in retractall

pl/preds.yap

@@ -489,6 +489,9 @@ retractall(V) :-
 	  '$do_error'(permission_error(modify,static_procedure,Na/Ar),retractall(T))
 	).
 	
+'$retractall_lu'(T,M) :-
+	'$free_arguments'(T), !,
+	( '$purge_clauses'(T,M), fail ; true ).
 '$retractall_lu'(T,M) :-
 	'$log_update_clause'(T,M,_,R),
 	erase(R),