def ids(type)

      Dir[File.join(dir_for(type), '**', '*.json')].collect { |path|
        File.basename(path, '.json')
      }.sort
    end
def ids(type)

      Dir[File.join(dir_for(type), '**', '*.json')].collect { |path|
        File.basename(path, '.json')
      }.sort
    end
Returns a sorted list of all the ids for a given type of documents.

 Warning : trusts the ids to be identical to the filenames