require type assertions when narrowing.

R=ken
OCL=24350
CL=24914
diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index 436ddd9..7ec215b 100644
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -827,9 +827,9 @@
 Node*	chanop(Node*, int);
 Node*	arrayop(Node*, int);
 Node*	ifaceop(Type*, Node*, int);
-int	ifaceas(Type*, Type*);
-int	ifaceas1(Type*, Type*);
-void	ifacecheck(Type*, Type*, int);
+int	ifaceas(Type*, Type*, int);
+int	ifaceas1(Type*, Type*, int);
+void	ifacecheck(Type*, Type*, int, int);
 void	runifacechecks(void);
 Node*	convas(Node*);
 void	arrayconv(Type*, Node*);