Handling case where opendir fails in directory-fold-tree.
Handling case where opendir fails in directory-fold-tree.

norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme,holmescn/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme,norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme