test: commentary for [h-m]*.go

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5674112
diff --git a/test/import5.go b/test/import5.go
index acd03c9..54d22fd 100644
--- a/test/import5.go
+++ b/test/import5.go
@@ -4,7 +4,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// import paths are slash-separated; reject backslash
+// Verify that imports with backslashes are rejected by the compiler.
+// Does not compile.
+// TODO: make more thorough.
 
 package main