        def cat(path, identifier=nil)
          p = CGI.escape(scm_iconv(@path_encoding, 'UTF-8', path))
          hg 'rhcat', '-r', CGI.escape(hgrev(identifier)), '--', hgtarget(p) do |io|
            io.binmode
            io.read
          end
        rescue HgCommandAborted
          nil  # means not found
        end