def root_dir(relpath)
      r = relpath.match(%r(^[/]?.+?[/$]))
      return relpath if r.nil?
      r[0] || relpath
    end
def root_dir(relpath)
      r = relpath.match(%r(^[/]?.+?[/$]))
      return relpath if r.nil?
      r[0] || relpath
    end
For a path relative such as 'x/y/z' returns 'x'. Useful for #mkdir_p
 where the entire new path is returned at once.