Fixing directory-fold to return knil on non-existing directories. Fixing file-regular?/directory?/... shortcut tests to return #f for non-existent files instead of a confusing error.
Fixing directory-fold to return knil on non-existing directories.
Fixing file-regular?/directory?/... shortcut tests to return #f
for non-existent files instead of a confusing error.

traviscross/chibi-scheme,traviscross/chibi-scheme,traviscross/chibi-scheme,traviscross/chibi-scheme