Support backup and restore of special files on POSIX style systems

Special files are device nodes and named pipes. The necessity of the
former is clear, the latter is debatable.
In order to preserve backward compatibility, the device number is
encoded in the StartChunk/StartOffset fields of the entry.

src/duplicacy_utils_windows.go

@@ -117,6 +117,14 @@ func (entry *Entry) SetAttributesToFile(fullPath string) {
 
 }
 
+func (entry *Entry) ReadDeviceNode(fileInfo os.FileInfo) bool {
+	return nil
+}
+
+func (entry *Entry) RestoreSpecial(fullPath string) error {
+	return nil
+}
+
 func joinPath(components ...string) string {
 
 	combinedPath := `\\?\` + filepath.Join(components...)