backend: Only return top-level files for most dirs

Fixes #1478

internal/backend/local/local.go

@@ -252,15 +252,27 @@ func (b *Local) List(ctx context.Context, t restic.FileType) <-chan string {
 	go func() {
 		defer close(ch)
 
-		err := fs.Walk(b.Basedir(t), func(path string, fi os.FileInfo, err error) error {
+		basedir, subdirs := b.Basedir(t)
+		err := fs.Walk(basedir, func(path string, fi os.FileInfo, err error) error {
+			debug.Log("walk on %v, %v\n", path, fi.IsDir())
 			if err != nil {
 				return err
 			}
 
+			if path == basedir {
+				return nil
+			}
+
 			if !isFile(fi) {
 				return nil
 			}
 
+			if fi.IsDir() && !subdirs {
+				return filepath.SkipDir
+			}
+
+			debug.Log("send %v\n", filepath.Base(path))
+
 			select {
 			case ch <- filepath.Base(path):
 			case <-ctx.Done():