newunionfs: sort ReadDir result

The previous code tried to make the result deterministic (See commit
74851f1), by always having the largest name at the end. This would
work for simple hashtable. Go does not use this, as discussed in
#476 (comment)

Use sort.Slice() to sort the entries by name.

Change-Id: Ibf576b00a214e38aa6bcd6b64ee6b9844408e04a

newunionfs/unionfs.go

@@ -11,6 +11,7 @@ import (
 	"io/ioutil"
 	"log"
 	"path/filepath"
+	"sort"
 	"syscall"
 
 	"github.com/hanwen/go-fuse/v2/fs"
@@ -346,29 +347,19 @@ func (n *unionFSNode) Readdir(ctx context.Context) (fs.DirStream, syscall.Errno)
 		// deepest root first.
 		readRoot(root.roots[len(root.roots)-i-1], dir, names)
 	}
-	result := make([]fuse.DirEntry, 0, 2*len(names))
-	maxIdx := -1
-	maxName := ""
+	result := make([]fuse.DirEntry, 0, len(names))
 	for nm, mode := range names {
 		marker := filePathHash(filepath.Join(dir, nm))
 		if _, ok := markers[marker]; ok {
 			continue
 		}
-		if nm > maxName {
-			maxName = nm
-			maxIdx = len(result)
-		}
 
 		result = append(result, fuse.DirEntry{
 			Name: nm,
 			Mode: mode,
 		})
 	}
-
-	if len(result) > 0 {
-		result = append(result[maxIdx:], result[:maxIdx]...)
-	}
-
+	sort.Slice(result, func(i, j int) bool { return result[i].Name < result[j].Name })
 	return fs.NewListDirStream(result), 0
 }