docs: def flatten_dir_tree(self, tree):
          """ Convert a file tree back into a flat dict """
  
          result = {}
  
          def helper(tree, leading_path = ''):
              dirs  = tree['dirs']; files = tree['files']
              for name, file_info in files.iteritems():
                  file_info['path'] = leading_path + '/'  + name
                  result[file_info['path']] = file_info
  
              for name, contents in dirs.iteritems():
                  helper(contents, leading_path +'/'+ name)
          helper(tree); return result