Add ERROR comment for errmsg to look for.

R=gri
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=19460
CL=19500
diff --git a/test/bugs/bug125.go b/test/bugs/bug125.go
index e2be164..c8c5f7d 100644
--- a/test/bugs/bug125.go
+++ b/test/bugs/bug125.go
@@ -8,7 +8,7 @@
 
 import (
 	OS "os"  // should require semicolon here; this is no different from other decls
-	IO "io"
+	IO "io"  // ERROR "missing"
 )
 
 func main() {