Ignore non-directories in the top level directory.

Ignore non-directories in the top level directory to allow placing a
README or similar file there.

flatfs.go

@@ -357,6 +357,16 @@ func (fs *Datastore) walk(path string, reschan chan query.Result) error {
 		return err
 	}
 	defer dir.Close()
+
+	// ignore non-directories
+	fileInfo, err := dir.Stat()
+	if err != nil {
+		return err
+	}
+	if !fileInfo.IsDir() {
+		return nil
+	}
+
 	names, err := dir.Readdirnames(-1)
 	if err != nil {
 		return err

flatfs_test.go

@@ -343,6 +343,11 @@ func testQuerySimple(dirFunc mkShardFunc, t *testing.T) {
 	temp, cleanup := tempdir(t)
 	defer cleanup()
 
+	err := ioutil.WriteFile(filepath.Join(temp, "README"), []byte("something"), 0666)
+	if err != nil {
+		t.Fatalf("WriteFile fail: %v\n", err)
+	}
+
 	fs, err := flatfs.New(temp, dirFunc(2), false)
 	if err != nil {
 		t.Fatalf("New fail: %v\n", err)