veyron/tools/gclogs: go 1.3.1 has a bug in the readdir code on macs.

Change-Id: I0dc90a4948b52c06ff5ff94bfde77b0a62ccc799
diff --git a/tools/gclogs/gclogs_test.go b/tools/gclogs/gclogs_test.go
index f9168fe..61b8058 100644
--- a/tools/gclogs/gclogs_test.go
+++ b/tools/gclogs/gclogs_test.go
@@ -1,5 +1,9 @@
+// +build -darwin
+
 package main
 
+// These tests need go 1.4 to run successfully on a mac.
+
 import (
 	"bytes"
 	"fmt"