saving new turn

pkg/repo/fs/fs.go

@@ -75,6 +75,10 @@ func (f *fs) Lock() (func() error, error) {
 	return unlock, nil
 }
 
+func (f *fs) Exist(path string) (bool, error) {
+	return fileExists(filepath.Join(f.root, path))
+}
+
 func (f *fs) Write(path string, v encoding.BinaryMarshaler) error {
 	if v == nil {
 		return errors.New("cant't marshal from nil object")