fails:File.realdirpath returns the real (absolute) pathname not containing symlinks
fails:File.realdirpath uses base directory for interpreting relative pathname
fails:File.realdirpath uses current directory for interpreting relative pathname
fails:File.realdirpath uses link directory for expanding relative links
fails:File.realdirpath raises an Errno::ELOOP if the symlink points to itself
fails:File.realdirpath raises Errno::ENOENT if the directory is absent
fails:File.realdirpath returns the real (absolute) pathname if the symlink points to an absent file
fails:File.realdirpath raises Errno::ENOENT if the symlink points to an absent directory
