new error messages

x.go:11: illegal types for operand: AS
	*I
	*T
	(*interface vs *struct)

R=r
DELTA=10  (8 added, 0 deleted, 2 changed)
OCL=21457
CL=21602

src/cmd/gc/go.h

@@ -351,10 +351,10 @@ enum
 	TFUNC,
 	TARRAY,
 	T_old_DARRAY,
-	TSTRUCT,
+	TSTRUCT,		// 23
 	TCHAN,
 	TMAP,
-	TINTER,
+	TINTER,			// 26
 	TFORW,
 	TFIELD,
 	TANY,

src/cmd/gc/subr.c

@@ -2140,6 +2140,14 @@ loop:
 		print("	%lT\n", tl);
 	if(tr != T)
 		print("	%lT\n", tr);
+
+	// common mistake: *struct and *interface.
+	if(tl && tr && isptr[tl->etype] && isptr[tr->etype]) {
+		if(tl->type->etype == TSTRUCT && tr->type->etype == TINTER)
+			print("	(*struct vs *interface)\n");
+		else if(tl->type->etype == TINTER && tr->type->etype == TSTRUCT)
+			print("	(*interface vs *struct)\n");
+	}
 }
 
 /*